Feature: RWDB (#378)

Co-authored-by: Denis Angell <dangell@transia.co>

Builds/CMake/RippledCore.cmake

@@ -538,7 +538,9 @@ target_sources (rippled PRIVATE
        subdir: nodestore
   #]===============================]
   src/ripple/nodestore/backend/CassandraFactory.cpp
+  src/ripple/nodestore/backend/RWDBFactory.cpp
   src/ripple/nodestore/backend/MemoryFactory.cpp
+  src/ripple/nodestore/backend/FlatmapFactory.cpp
   src/ripple/nodestore/backend/NuDBFactory.cpp
   src/ripple/nodestore/backend/NullFactory.cpp
   src/ripple/nodestore/backend/RocksDBFactory.cpp

cfg/rippled-example.cfg

@@ -1056,7 +1056,18 @@
 #       Cassandra is an alternative backend to be used only with Reporting Mode.
 #       See the Reporting Mode section for more details about Reporting Mode.
 #
-#   Required keys for NuDB and RocksDB:
+#   type = RWDB
+#
+#       RWDB is a high-performance memory store written by XRPL-Labs and optimized
+#       for xahaud. RWDB is NOT persistent and the data will be lost on restart.
+#       RWDB is recommended for Validator and Peer nodes that are not required to 
+#       store history.
+#
+#       RWDB maintains its high speed regardless of the amount of history
+#       stored. Online delete should NOT be used instead RWDB will use the 
+#       ledger_history config value to determine how many ledgers to keep in memory.
+#
+#   Required keys for NuDB, RWDB and RocksDB:
 #
 #       path                Location to store the database
 #
@@ -1112,7 +1123,8 @@
 #       online_delete       Minimum value of 256. Enable automatic purging
 #                           of older ledger information. Maintain at least this
 #                           number of ledger records online. Must be greater
-#                           than or equal to ledger_history.
+#                           than or equal to ledger_history. If using RWDB 
+#                           this value is ignored.
 #
 #       These keys modify the behavior of online_delete, and thus are only
 #       relevant if online_delete is defined and non-zero:

src/ripple/app/ledger/impl/LedgerCleaner.cpp

@@ -219,7 +219,7 @@ private:
     run()
     {
         beast::setCurrentThreadName("LedgerCleaner");
-        JLOG(j_.debug()) << "Started";
+        JLOG(j_.debug()) << "Started ledger cleaner";
 
         while (true)
         {
@@ -392,7 +392,8 @@ private:
 
             if (app_.getFeeTrack().isLoadedLocal())
             {
-                JLOG(j_.debug()) << "Waiting for load to subside";
+                JLOG(j_.debug())
+                    << "Ledger Cleaner: Waiting for load to subside";
                 std::this_thread::sleep_for(std::chrono::seconds(5));
                 continue;
             }
@@ -415,13 +416,15 @@ private:
             bool fail = false;
             if (ledgerHash.isZero())
             {
-                JLOG(j_.info())
-                    << "Unable to get hash for ledger " << ledgerIndex;
+                JLOG(j_.warn())
+                    << "Ledger Cleaner: Unable to get hash for ledger "
+                    << ledgerIndex;
                 fail = true;
             }
             else if (!doLedger(ledgerIndex, ledgerHash, doNodes, doTxns))
             {
-                JLOG(j_.info()) << "Failed to process ledger " << ledgerIndex;
+                JLOG(j_.warn()) << "Ledger Cleaner: Failed to process ledger "
+                                << ledgerIndex;
                 fail = true;
             }
 

src/ripple/app/main/Application.h

@@ -19,7 +19,6 @@
 
 #ifndef RIPPLE_APP_MAIN_APPLICATION_H_INCLUDED
 #define RIPPLE_APP_MAIN_APPLICATION_H_INCLUDED
-
 #include <ripple/basics/TaggedCache.h>
 #include <ripple/beast/utility/PropertyStream.h>
 #include <ripple/core/Config.h>

src/ripple/app/misc/SHAMapStoreImp.cpp

@@ -118,7 +118,9 @@ SHAMapStoreImp::SHAMapStoreImp(
 
     get_if_exists(section, "online_delete", deleteInterval_);
 
-    if (deleteInterval_)
+    bool const isMem = config.mem_backend();
+
+    if (deleteInterval_ || isMem)
     {
         if (app_.config().reporting())
         {
@@ -127,6 +129,9 @@ SHAMapStoreImp::SHAMapStoreImp(
                 "online_delete info from config");
         }
 
+        if (isMem)
+            deleteInterval_ = config.LEDGER_HISTORY;
+
         // Configuration that affects the behavior of online delete
         get_if_exists(section, "delete_batch", deleteBatch_);
         std::uint32_t temp;
@@ -162,7 +167,8 @@ SHAMapStoreImp::SHAMapStoreImp(
         }
 
         state_db_.init(config, dbName_);
-        dbPaths();
+        if (!isMem)
+            dbPaths();
     }
 }
 
@@ -195,6 +201,7 @@ SHAMapStoreImp::makeNodeStore(int readThreads)
                 "online_delete info from config");
         }
         SavedState state = state_db_.getState();
+
         auto writableBackend = makeBackendRotating(state.writableDb);
         auto archiveBackend = makeBackendRotating(state.archiveDb);
         if (!state.writableDb.size())
@@ -293,6 +300,8 @@ SHAMapStoreImp::run()
     fullBelowCache_ = &(*app_.getNodeFamily().getFullBelowCache(0));
     treeNodeCache_ = &(*app_.getNodeFamily().getTreeNodeCache(0));
 
+    bool const isMem = app_.config().mem_backend();
+
     if (advisoryDelete_)
         canDelete_ = state_db_.getCanDelete();
 
@@ -351,7 +360,7 @@ SHAMapStoreImp::run()
         // will delete up to (not including) lastRotated
         if (readyToRotate && !waitForImport)
         {
-            JLOG(journal_.warn())
+            JLOG(journal_.debug())
                 << "rotating  validatedSeq " << validatedSeq << " lastRotated "
                 << lastRotated << " deleteInterval " << deleteInterval_
                 << " canDelete_ " << canDelete_ << " state "
@@ -395,7 +404,7 @@ SHAMapStoreImp::run()
             // Only log if we completed without a "health" abort
             JLOG(journal_.debug()) << validatedSeq << " freshened caches";
 
-            JLOG(journal_.trace()) << "Making a new backend";
+            JLOG(journal_.debug()) << "Making a new backend";
             auto newBackend = makeBackendRotating();
             JLOG(journal_.debug())
                 << validatedSeq << " new backend " << newBackend->getName();

src/ripple/app/rdb/backend/FlatmapDatabase.h

@@ -0,0 +1,853 @@
+#ifndef RIPPLE_APP_RDB_BACKEND_FLATMAPDATABASE_H_INCLUDED
+#define RIPPLE_APP_RDB_BACKEND_FLATMAPDATABASE_H_INCLUDED
+
+#include <ripple/app/ledger/AcceptedLedger.h>
+#include <ripple/app/ledger/LedgerMaster.h>
+#include <ripple/app/ledger/TransactionMaster.h>
+#include <ripple/app/rdb/backend/SQLiteDatabase.h>
+#include <algorithm>
+#include <map>
+#include <mutex>
+#include <optional>
+#include <shared_mutex>
+#include <vector>
+
+#include <boost/unordered/concurrent_flat_map.hpp>
+
+namespace ripple {
+
+struct base_uint_hasher
+{
+    using result_type = std::size_t;
+
+    result_type
+    operator()(base_uint<256> const& value) const
+    {
+        return hardened_hash<>{}(value);
+    }
+
+    result_type
+    operator()(AccountID const& value) const
+    {
+        return hardened_hash<>{}(value);
+    }
+};
+
+class FlatmapDatabase : public SQLiteDatabase
+{
+private:
+    struct LedgerData
+    {
+        LedgerInfo info;
+        boost::unordered::
+            concurrent_flat_map<uint256, AccountTx, base_uint_hasher>
+                transactions;
+    };
+
+    struct AccountTxData
+    {
+        boost::unordered::
+            concurrent_flat_map<std::pair<uint32_t, uint32_t>, AccountTx>
+                transactions;
+    };
+
+    Application& app_;
+    Config const& config_;
+    JobQueue& jobQueue_;
+
+    boost::unordered::concurrent_flat_map<LedgerIndex, LedgerData> ledgers_;
+    boost::unordered::
+        concurrent_flat_map<uint256, LedgerIndex, base_uint_hasher>
+            ledgerHashToSeq_;
+    boost::unordered::concurrent_flat_map<uint256, AccountTx, base_uint_hasher>
+        transactionMap_;
+    boost::unordered::
+        concurrent_flat_map<AccountID, AccountTxData, base_uint_hasher>
+            accountTxMap_;
+
+public:
+    FlatmapDatabase(Application& app, Config const& config, JobQueue& jobQueue)
+        : app_(app), config_(config), jobQueue_(jobQueue)
+    {
+    }
+
+    std::optional<LedgerIndex>
+    getMinLedgerSeq() override
+    {
+        std::optional<LedgerIndex> minSeq;
+        ledgers_.visit_all([&minSeq](auto const& pair) {
+            if (!minSeq || pair.first < *minSeq)
+            {
+                minSeq = pair.first;
+            }
+        });
+        return minSeq;
+    }
+
+    std::optional<LedgerIndex>
+    getTransactionsMinLedgerSeq() override
+    {
+        std::optional<LedgerIndex> minSeq;
+        transactionMap_.visit_all([&minSeq](auto const& pair) {
+            LedgerIndex seq = pair.second.second->getLgrSeq();
+            if (!minSeq || seq < *minSeq)
+            {
+                minSeq = seq;
+            }
+        });
+        return minSeq;
+    }
+
+    std::optional<LedgerIndex>
+    getAccountTransactionsMinLedgerSeq() override
+    {
+        std::optional<LedgerIndex> minSeq;
+        accountTxMap_.visit_all([&minSeq](auto const& pair) {
+            pair.second.transactions.visit_all([&minSeq](auto const& tx) {
+                if (!minSeq || tx.first.first < *minSeq)
+                {
+                    minSeq = tx.first.first;
+                }
+            });
+        });
+        return minSeq;
+    }
+
+    std::optional<LedgerIndex>
+    getMaxLedgerSeq() override
+    {
+        std::optional<LedgerIndex> maxSeq;
+        ledgers_.visit_all([&maxSeq](auto const& pair) {
+            if (!maxSeq || pair.first > *maxSeq)
+            {
+                maxSeq = pair.first;
+            }
+        });
+        return maxSeq;
+    }
+    void
+    deleteTransactionByLedgerSeq(LedgerIndex ledgerSeq) override
+    {
+        ledgers_.visit(ledgerSeq, [this](auto& item) {
+            item.second.transactions.visit_all([this](auto const& txPair) {
+                transactionMap_.erase(txPair.first);
+            });
+            item.second.transactions.clear();
+        });
+
+        accountTxMap_.visit_all([ledgerSeq](auto& item) {
+            item.second.transactions.erase_if([ledgerSeq](auto const& tx) {
+                return tx.first.first == ledgerSeq;
+            });
+        });
+    }
+
+    void
+    deleteBeforeLedgerSeq(LedgerIndex ledgerSeq) override
+    {
+        ledgers_.erase_if([this, ledgerSeq](auto const& item) {
+            if (item.first < ledgerSeq)
+            {
+                item.second.transactions.visit_all([this](auto const& txPair) {
+                    transactionMap_.erase(txPair.first);
+                });
+                ledgerHashToSeq_.erase(item.second.info.hash);
+                return true;
+            }
+            return false;
+        });
+
+        accountTxMap_.visit_all([ledgerSeq](auto& item) {
+            item.second.transactions.erase_if([ledgerSeq](auto const& tx) {
+                return tx.first.first < ledgerSeq;
+            });
+        });
+    }
+
+    void
+    deleteTransactionsBeforeLedgerSeq(LedgerIndex ledgerSeq) override
+    {
+        ledgers_.visit_all([this, ledgerSeq](auto& item) {
+            if (item.first < ledgerSeq)
+            {
+                item.second.transactions.visit_all([this](auto const& txPair) {
+                    transactionMap_.erase(txPair.first);
+                });
+                item.second.transactions.clear();
+            }
+        });
+
+        accountTxMap_.visit_all([ledgerSeq](auto& item) {
+            item.second.transactions.erase_if([ledgerSeq](auto const& tx) {
+                return tx.first.first < ledgerSeq;
+            });
+        });
+    }
+
+    void
+    deleteAccountTransactionsBeforeLedgerSeq(LedgerIndex ledgerSeq) override
+    {
+        accountTxMap_.visit_all([ledgerSeq](auto& item) {
+            item.second.transactions.erase_if([ledgerSeq](auto const& tx) {
+                return tx.first.first < ledgerSeq;
+            });
+        });
+    }
+    std::size_t
+    getTransactionCount() override
+    {
+        return transactionMap_.size();
+    }
+
+    std::size_t
+    getAccountTransactionCount() override
+    {
+        std::size_t count = 0;
+        accountTxMap_.visit_all([&count](auto const& item) {
+            count += item.second.transactions.size();
+        });
+        return count;
+    }
+
+    CountMinMax
+    getLedgerCountMinMax() override
+    {
+        CountMinMax result{0, 0, 0};
+        ledgers_.visit_all([&result](auto const& item) {
+            result.numberOfRows++;
+            if (result.minLedgerSequence == 0 ||
+                item.first < result.minLedgerSequence)
+            {
+                result.minLedgerSequence = item.first;
+            }
+            if (item.first > result.maxLedgerSequence)
+            {
+                result.maxLedgerSequence = item.first;
+            }
+        });
+        return result;
+    }
+
+    bool
+    saveValidatedLedger(
+        std::shared_ptr<Ledger const> const& ledger,
+        bool current) override
+    {
+        try
+        {
+            LedgerData ledgerData;
+            ledgerData.info = ledger->info();
+
+            auto aLedger = std::make_shared<AcceptedLedger>(ledger, app_);
+            for (auto const& acceptedLedgerTx : *aLedger)
+            {
+                auto const& txn = acceptedLedgerTx->getTxn();
+                auto const& meta = acceptedLedgerTx->getMeta();
+                auto const& id = txn->getTransactionID();
+
+                std::string reason;
+                auto accTx = std::make_pair(
+                    std::make_shared<ripple::Transaction>(txn, reason, app_),
+                    std::make_shared<ripple::TxMeta>(meta));
+
+                ledgerData.transactions.emplace(id, accTx);
+                transactionMap_.emplace(id, accTx);
+
+                for (auto const& account : meta.getAffectedAccounts())
+                {
+                    accountTxMap_.visit(account, [&](auto& data) {
+                        data.second.transactions.emplace(
+                            std::make_pair(
+                                ledger->info().seq,
+                                acceptedLedgerTx->getTxnSeq()),
+                            accTx);
+                    });
+                }
+            }
+
+            ledgers_.emplace(ledger->info().seq, std::move(ledgerData));
+            ledgerHashToSeq_.emplace(ledger->info().hash, ledger->info().seq);
+
+            if (current)
+            {
+                auto const cutoffSeq =
+                    ledger->info().seq > app_.config().LEDGER_HISTORY
+                    ? ledger->info().seq - app_.config().LEDGER_HISTORY
+                    : 0;
+
+                if (cutoffSeq > 0)
+                {
+                    const std::size_t BATCH_SIZE = 128;
+                    std::size_t deleted = 0;
+
+                    ledgers_.erase_if([&](auto const& item) {
+                        if (deleted >= BATCH_SIZE)
+                            return false;
+
+                        if (item.first < cutoffSeq)
+                        {
+                            item.second.transactions.visit_all(
+                                [this](auto const& txPair) {
+                                    transactionMap_.erase(txPair.first);
+                                });
+                            ledgerHashToSeq_.erase(item.second.info.hash);
+                            deleted++;
+                            return true;
+                        }
+                        return false;
+                    });
+
+                    if (deleted > 0)
+                    {
+                        accountTxMap_.visit_all([cutoffSeq](auto& item) {
+                            item.second.transactions.erase_if(
+                                [cutoffSeq](auto const& tx) {
+                                    return tx.first.first < cutoffSeq;
+                                });
+                        });
+                    }
+
+                    app_.getLedgerMaster().clearPriorLedgers(cutoffSeq);
+                }
+            }
+
+            return true;
+        }
+        catch (std::exception const&)
+        {
+            deleteTransactionByLedgerSeq(ledger->info().seq);
+            return false;
+        }
+    }
+
+    std::optional<LedgerInfo>
+    getLedgerInfoByIndex(LedgerIndex ledgerSeq) override
+    {
+        std::optional<LedgerInfo> result;
+        ledgers_.visit(ledgerSeq, [&result](auto const& item) {
+            result = item.second.info;
+        });
+        return result;
+    }
+
+    std::optional<LedgerInfo>
+    getNewestLedgerInfo() override
+    {
+        std::optional<LedgerInfo> result;
+        ledgers_.visit_all([&result](auto const& item) {
+            if (!result || item.second.info.seq > result->seq)
+            {
+                result = item.second.info;
+            }
+        });
+        return result;
+    }
+
+    std::optional<LedgerInfo>
+    getLimitedOldestLedgerInfo(LedgerIndex ledgerFirstIndex) override
+    {
+        std::optional<LedgerInfo> result;
+        ledgers_.visit_all([&](auto const& item) {
+            if (item.first >= ledgerFirstIndex &&
+                (!result || item.first < result->seq))
+            {
+                result = item.second.info;
+            }
+        });
+        return result;
+    }
+
+    std::optional<LedgerInfo>
+    getLimitedNewestLedgerInfo(LedgerIndex ledgerFirstIndex) override
+    {
+        std::optional<LedgerInfo> result;
+        ledgers_.visit_all([&](auto const& item) {
+            if (item.first >= ledgerFirstIndex &&
+                (!result || item.first > result->seq))
+            {
+                result = item.second.info;
+            }
+        });
+        return result;
+    }
+
+    std::optional<LedgerInfo>
+    getLedgerInfoByHash(uint256 const& ledgerHash) override
+    {
+        std::optional<LedgerInfo> result;
+        ledgerHashToSeq_.visit(ledgerHash, [this, &result](auto const& item) {
+            ledgers_.visit(item.second, [&result](auto const& item) {
+                result = item.second.info;
+            });
+        });
+        return result;
+    }
+    uint256
+    getHashByIndex(LedgerIndex ledgerIndex) override
+    {
+        uint256 result;
+        ledgers_.visit(ledgerIndex, [&result](auto const& item) {
+            result = item.second.info.hash;
+        });
+        return result;
+    }
+
+    std::optional<LedgerHashPair>
+    getHashesByIndex(LedgerIndex ledgerIndex) override
+    {
+        std::optional<LedgerHashPair> result;
+        ledgers_.visit(ledgerIndex, [&result](auto const& item) {
+            result = LedgerHashPair{
+                item.second.info.hash, item.second.info.parentHash};
+        });
+        return result;
+    }
+
+    std::map<LedgerIndex, LedgerHashPair>
+    getHashesByIndex(LedgerIndex minSeq, LedgerIndex maxSeq) override
+    {
+        std::map<LedgerIndex, LedgerHashPair> result;
+        ledgers_.visit_all([&](auto const& item) {
+            if (item.first >= minSeq && item.first <= maxSeq)
+            {
+                result[item.first] = LedgerHashPair{
+                    item.second.info.hash, item.second.info.parentHash};
+            }
+        });
+        return result;
+    }
+
+    std::variant<AccountTx, TxSearched>
+    getTransaction(
+        uint256 const& id,
+        std::optional<ClosedInterval<std::uint32_t>> const& range,
+        error_code_i& ec) override
+    {
+        std::variant<AccountTx, TxSearched> result = TxSearched::unknown;
+        transactionMap_.visit(id, [&](auto const& item) {
+            auto const& tx = item.second;
+            if (!range ||
+                (range->lower() <= tx.second->getLgrSeq() &&
+                 tx.second->getLgrSeq() <= range->upper()))
+            {
+                result = tx;
+            }
+            else
+            {
+                result = TxSearched::all;
+            }
+        });
+        return result;
+    }
+
+    bool
+    ledgerDbHasSpace(Config const& config) override
+    {
+        return true;  // In-memory database always has space
+    }
+
+    bool
+    transactionDbHasSpace(Config const& config) override
+    {
+        return true;  // In-memory database always has space
+    }
+
+    std::uint32_t
+    getKBUsedAll() override
+    {
+        std::uint32_t size = sizeof(*this);
+        size += ledgers_.size() * (sizeof(LedgerIndex) + sizeof(LedgerData));
+        size +=
+            ledgerHashToSeq_.size() * (sizeof(uint256) + sizeof(LedgerIndex));
+        size += transactionMap_.size() * (sizeof(uint256) + sizeof(AccountTx));
+        accountTxMap_.visit_all([&size](auto const& item) {
+            size += sizeof(AccountID) + sizeof(AccountTxData);
+            size += item.second.transactions.size() * sizeof(AccountTx);
+        });
+        return size / 1024;  // Convert to KB
+    }
+
+    std::uint32_t
+    getKBUsedLedger() override
+    {
+        std::uint32_t size =
+            ledgers_.size() * (sizeof(LedgerIndex) + sizeof(LedgerData));
+        size +=
+            ledgerHashToSeq_.size() * (sizeof(uint256) + sizeof(LedgerIndex));
+        return size / 1024;
+    }
+
+    std::uint32_t
+    getKBUsedTransaction() override
+    {
+        std::uint32_t size =
+            transactionMap_.size() * (sizeof(uint256) + sizeof(AccountTx));
+        accountTxMap_.visit_all([&size](auto const& item) {
+            size += sizeof(AccountID) + sizeof(AccountTxData);
+            size += item.second.transactions.size() * sizeof(AccountTx);
+        });
+        return size / 1024;
+    }
+
+    void
+    closeLedgerDB() override
+    {
+        // No-op for in-memory database
+    }
+
+    void
+    closeTransactionDB() override
+    {
+        // No-op for in-memory database
+    }
+
+    ~FlatmapDatabase()
+    {
+        // Concurrent maps need visit_all
+        accountTxMap_.visit_all(
+            [](auto& pair) { pair.second.transactions.clear(); });
+        accountTxMap_.clear();
+
+        transactionMap_.clear();
+
+        ledgers_.visit_all(
+            [](auto& pair) { pair.second.transactions.clear(); });
+        ledgers_.clear();
+
+        ledgerHashToSeq_.clear();
+    }
+
+    std::vector<std::shared_ptr<Transaction>>
+    getTxHistory(LedgerIndex startIndex) override
+    {
+        std::vector<std::shared_ptr<Transaction>> result;
+        transactionMap_.visit_all([&](auto const& item) {
+            if (item.second.second->getLgrSeq() >= startIndex)
+            {
+                result.push_back(item.second.first);
+            }
+        });
+        std::sort(
+            result.begin(), result.end(), [](auto const& a, auto const& b) {
+                return a->getLedger() > b->getLedger();
+            });
+        if (result.size() > 20)
+        {
+            result.resize(20);
+        }
+        return result;
+    }
+    // Helper function to handle limits
+    template <typename Container>
+    void
+    applyLimit(Container& container, std::size_t limit, bool bUnlimited)
+    {
+        if (!bUnlimited && limit > 0 && container.size() > limit)
+        {
+            container.resize(limit);
+        }
+    }
+
+    AccountTxs
+    getOldestAccountTxs(AccountTxOptions const& options) override
+    {
+        AccountTxs result;
+        accountTxMap_.visit(options.account, [&](auto const& item) {
+            item.second.transactions.visit_all([&](auto const& tx) {
+                if (tx.first.first >= options.minLedger &&
+                    tx.first.first <= options.maxLedger)
+                {
+                    result.push_back(tx.second);
+                }
+            });
+        });
+        std::sort(
+            result.begin(), result.end(), [](auto const& a, auto const& b) {
+                return a.second->getLgrSeq() < b.second->getLgrSeq();
+            });
+        applyLimit(result, options.limit, options.bUnlimited);
+        return result;
+    }
+
+    AccountTxs
+    getNewestAccountTxs(AccountTxOptions const& options) override
+    {
+        AccountTxs result;
+        accountTxMap_.visit(options.account, [&](auto const& item) {
+            item.second.transactions.visit_all([&](auto const& tx) {
+                if (tx.first.first >= options.minLedger &&
+                    tx.first.first <= options.maxLedger)
+                {
+                    result.push_back(tx.second);
+                }
+            });
+        });
+        std::sort(
+            result.begin(), result.end(), [](auto const& a, auto const& b) {
+                return a.second->getLgrSeq() > b.second->getLgrSeq();
+            });
+        applyLimit(result, options.limit, options.bUnlimited);
+        return result;
+    }
+
+    MetaTxsList
+    getOldestAccountTxsB(AccountTxOptions const& options) override
+    {
+        MetaTxsList result;
+        accountTxMap_.visit(options.account, [&](auto const& item) {
+            item.second.transactions.visit_all([&](auto const& tx) {
+                if (tx.first.first >= options.minLedger &&
+                    tx.first.first <= options.maxLedger)
+                {
+                    result.emplace_back(
+                        tx.second.first->getSTransaction()
+                            ->getSerializer()
+                            .peekData(),
+                        tx.second.second->getAsObject()
+                            .getSerializer()
+                            .peekData(),
+                        tx.first.first);
+                }
+            });
+        });
+        std::sort(
+            result.begin(), result.end(), [](auto const& a, auto const& b) {
+                return std::get<2>(a) < std::get<2>(b);
+            });
+        applyLimit(result, options.limit, options.bUnlimited);
+        return result;
+    }
+
+    MetaTxsList
+    getNewestAccountTxsB(AccountTxOptions const& options) override
+    {
+        MetaTxsList result;
+        accountTxMap_.visit(options.account, [&](auto const& item) {
+            item.second.transactions.visit_all([&](auto const& tx) {
+                if (tx.first.first >= options.minLedger &&
+                    tx.first.first <= options.maxLedger)
+                {
+                    result.emplace_back(
+                        tx.second.first->getSTransaction()
+                            ->getSerializer()
+                            .peekData(),
+                        tx.second.second->getAsObject()
+                            .getSerializer()
+                            .peekData(),
+                        tx.first.first);
+                }
+            });
+        });
+        std::sort(
+            result.begin(), result.end(), [](auto const& a, auto const& b) {
+                return std::get<2>(a) > std::get<2>(b);
+            });
+        applyLimit(result, options.limit, options.bUnlimited);
+        return result;
+    }
+    std::pair<AccountTxs, std::optional<AccountTxMarker>>
+    oldestAccountTxPage(AccountTxPageOptions const& options) override
+    {
+        AccountTxs result;
+        std::optional<AccountTxMarker> marker;
+
+        accountTxMap_.visit(options.account, [&](auto const& item) {
+            std::vector<std::pair<std::pair<uint32_t, uint32_t>, AccountTx>>
+                txs;
+            item.second.transactions.visit_all([&](auto const& tx) {
+                if (tx.first.first >= options.minLedger &&
+                    tx.first.first <= options.maxLedger)
+                {
+                    txs.emplace_back(tx);
+                }
+            });
+
+            std::sort(txs.begin(), txs.end(), [](auto const& a, auto const& b) {
+                return a.first < b.first;
+            });
+
+            auto it = txs.begin();
+            if (options.marker)
+            {
+                it = std::find_if(txs.begin(), txs.end(), [&](auto const& tx) {
+                    return tx.first.first == options.marker->ledgerSeq &&
+                        tx.first.second == options.marker->txnSeq;
+                });
+                if (it != txs.end())
+                    ++it;
+            }
+
+            for (; it != txs.end() &&
+                 (options.limit == 0 || result.size() < options.limit);
+                 ++it)
+            {
+                result.push_back(it->second);
+            }
+
+            if (it != txs.end())
+            {
+                marker = AccountTxMarker{it->first.first, it->first.second};
+            }
+        });
+
+        return {result, marker};
+    }
+
+    std::pair<AccountTxs, std::optional<AccountTxMarker>>
+    newestAccountTxPage(AccountTxPageOptions const& options) override
+    {
+        AccountTxs result;
+        std::optional<AccountTxMarker> marker;
+
+        accountTxMap_.visit(options.account, [&](auto const& item) {
+            std::vector<std::pair<std::pair<uint32_t, uint32_t>, AccountTx>>
+                txs;
+            item.second.transactions.visit_all([&](auto const& tx) {
+                if (tx.first.first >= options.minLedger &&
+                    tx.first.first <= options.maxLedger)
+                {
+                    txs.emplace_back(tx);
+                }
+            });
+
+            std::sort(txs.begin(), txs.end(), [](auto const& a, auto const& b) {
+                return a.first > b.first;
+            });
+
+            auto it = txs.begin();
+            if (options.marker)
+            {
+                it = std::find_if(txs.begin(), txs.end(), [&](auto const& tx) {
+                    return tx.first.first == options.marker->ledgerSeq &&
+                        tx.first.second == options.marker->txnSeq;
+                });
+                if (it != txs.end())
+                    ++it;
+            }
+
+            for (; it != txs.end() &&
+                 (options.limit == 0 || result.size() < options.limit);
+                 ++it)
+            {
+                result.push_back(it->second);
+            }
+
+            if (it != txs.end())
+            {
+                marker = AccountTxMarker{it->first.first, it->first.second};
+            }
+        });
+
+        return {result, marker};
+    }
+
+    std::pair<MetaTxsList, std::optional<AccountTxMarker>>
+    oldestAccountTxPageB(AccountTxPageOptions const& options) override
+    {
+        MetaTxsList result;
+        std::optional<AccountTxMarker> marker;
+
+        accountTxMap_.visit(options.account, [&](auto const& item) {
+            std::vector<std::tuple<uint32_t, uint32_t, AccountTx>> txs;
+            item.second.transactions.visit_all([&](auto const& tx) {
+                if (tx.first.first >= options.minLedger &&
+                    tx.first.first <= options.maxLedger)
+                {
+                    txs.emplace_back(
+                        tx.first.first, tx.first.second, tx.second);
+                }
+            });
+
+            std::sort(txs.begin(), txs.end());
+
+            auto it = txs.begin();
+            if (options.marker)
+            {
+                it = std::find_if(txs.begin(), txs.end(), [&](auto const& tx) {
+                    return std::get<0>(tx) == options.marker->ledgerSeq &&
+                        std::get<1>(tx) == options.marker->txnSeq;
+                });
+                if (it != txs.end())
+                    ++it;
+            }
+
+            for (; it != txs.end() &&
+                 (options.limit == 0 || result.size() < options.limit);
+                 ++it)
+            {
+                const auto& [_, __, tx] = *it;
+                result.emplace_back(
+                    tx.first->getSTransaction()->getSerializer().peekData(),
+                    tx.second->getAsObject().getSerializer().peekData(),
+                    std::get<0>(*it));
+            }
+
+            if (it != txs.end())
+            {
+                marker = AccountTxMarker{std::get<0>(*it), std::get<1>(*it)};
+            }
+        });
+
+        return {result, marker};
+    }
+
+    std::pair<MetaTxsList, std::optional<AccountTxMarker>>
+    newestAccountTxPageB(AccountTxPageOptions const& options) override
+    {
+        MetaTxsList result;
+        std::optional<AccountTxMarker> marker;
+
+        accountTxMap_.visit(options.account, [&](auto const& item) {
+            std::vector<std::tuple<uint32_t, uint32_t, AccountTx>> txs;
+            item.second.transactions.visit_all([&](auto const& tx) {
+                if (tx.first.first >= options.minLedger &&
+                    tx.first.first <= options.maxLedger)
+                {
+                    txs.emplace_back(
+                        tx.first.first, tx.first.second, tx.second);
+                }
+            });
+
+            std::sort(txs.begin(), txs.end(), std::greater<>());
+
+            auto it = txs.begin();
+            if (options.marker)
+            {
+                it = std::find_if(txs.begin(), txs.end(), [&](auto const& tx) {
+                    return std::get<0>(tx) == options.marker->ledgerSeq &&
+                        std::get<1>(tx) == options.marker->txnSeq;
+                });
+                if (it != txs.end())
+                    ++it;
+            }
+
+            for (; it != txs.end() &&
+                 (options.limit == 0 || result.size() < options.limit);
+                 ++it)
+            {
+                const auto& [_, __, tx] = *it;
+                result.emplace_back(
+                    tx.first->getSTransaction()->getSerializer().peekData(),
+                    tx.second->getAsObject().getSerializer().peekData(),
+                    std::get<0>(*it));
+            }
+
+            if (it != txs.end())
+            {
+                marker = AccountTxMarker{std::get<0>(*it), std::get<1>(*it)};
+            }
+        });
+
+        return {result, marker};
+    }
+};
+
+// Factory function
+std::unique_ptr<SQLiteDatabase>
+getFlatmapDatabase(Application& app, Config const& config, JobQueue& jobQueue)
+{
+    return std::make_unique<FlatmapDatabase>(app, config, jobQueue);
+}
+
+}  // namespace ripple
+#endif  // RIPPLE_APP_RDB_BACKEND_FLATMAPDATABASE_H_INCLUDED

src/ripple/app/rdb/backend/RWDBDatabase.h

@@ -0,0 +1,964 @@
+#ifndef RIPPLE_APP_RDB_BACKEND_MEMORYDATABASE_H_INCLUDED
+#define RIPPLE_APP_RDB_BACKEND_MEMORYDATABASE_H_INCLUDED
+
+#include <ripple/app/ledger/AcceptedLedger.h>
+#include <ripple/app/ledger/LedgerMaster.h>
+#include <ripple/app/ledger/TransactionMaster.h>
+#include <ripple/app/rdb/backend/SQLiteDatabase.h>
+#include <algorithm>
+#include <map>
+#include <mutex>
+#include <optional>
+#include <shared_mutex>
+#include <vector>
+
+namespace ripple {
+
+class RWDBDatabase : public SQLiteDatabase
+{
+private:
+    struct LedgerData
+    {
+        LedgerInfo info;
+        std::map<uint256, AccountTx> transactions;
+    };
+
+    struct AccountTxData
+    {
+        AccountTxs transactions;
+        std::map<uint32_t, std::map<uint32_t, size_t>>
+            ledgerTxMap;  // ledgerSeq -> txSeq -> index in transactions
+    };
+
+    Application& app_;
+
+    mutable std::shared_mutex mutex_;
+
+    std::map<LedgerIndex, LedgerData> ledgers_;
+    std::map<uint256, LedgerIndex> ledgerHashToSeq_;
+    std::map<uint256, AccountTx> transactionMap_;
+    std::map<AccountID, AccountTxData> accountTxMap_;
+
+public:
+    RWDBDatabase(Application& app, Config const& config, JobQueue& jobQueue)
+        : app_(app)
+    {
+    }
+
+    std::optional<LedgerIndex>
+    getMinLedgerSeq() override
+    {
+        std::shared_lock<std::shared_mutex> lock(mutex_);
+        if (ledgers_.empty())
+            return std::nullopt;
+        return ledgers_.begin()->first;
+    }
+
+    std::optional<LedgerIndex>
+    getTransactionsMinLedgerSeq() override
+    {
+        std::shared_lock<std::shared_mutex> lock(mutex_);
+        if (transactionMap_.empty())
+            return std::nullopt;
+        return transactionMap_.begin()->second.second->getLgrSeq();
+    }
+
+    std::optional<LedgerIndex>
+    getAccountTransactionsMinLedgerSeq() override
+    {
+        std::shared_lock<std::shared_mutex> lock(mutex_);
+        if (accountTxMap_.empty())
+            return std::nullopt;
+        LedgerIndex minSeq = std::numeric_limits<LedgerIndex>::max();
+        for (const auto& [_, accountData] : accountTxMap_)
+        {
+            if (!accountData.ledgerTxMap.empty())
+                minSeq =
+                    std::min(minSeq, accountData.ledgerTxMap.begin()->first);
+        }
+        return minSeq == std::numeric_limits<LedgerIndex>::max()
+            ? std::nullopt
+            : std::optional<LedgerIndex>(minSeq);
+    }
+
+    std::optional<LedgerIndex>
+    getMaxLedgerSeq() override
+    {
+        std::shared_lock<std::shared_mutex> lock(mutex_);
+        if (ledgers_.empty())
+            return std::nullopt;
+        return ledgers_.rbegin()->first;
+    }
+    void
+    deleteTransactionByLedgerSeq(LedgerIndex ledgerSeq) override
+    {
+        std::unique_lock<std::shared_mutex> lock(mutex_);
+        auto it = ledgers_.find(ledgerSeq);
+        if (it != ledgers_.end())
+        {
+            for (const auto& [txHash, _] : it->second.transactions)
+            {
+                transactionMap_.erase(txHash);
+            }
+            it->second.transactions.clear();
+        }
+        for (auto& [_, accountData] : accountTxMap_)
+        {
+            accountData.ledgerTxMap.erase(ledgerSeq);
+            accountData.transactions.erase(
+                std::remove_if(
+                    accountData.transactions.begin(),
+                    accountData.transactions.end(),
+                    [ledgerSeq](const AccountTx& tx) {
+                        return tx.second->getLgrSeq() == ledgerSeq;
+                    }),
+                accountData.transactions.end());
+        }
+    }
+
+    void
+    deleteBeforeLedgerSeq(LedgerIndex ledgerSeq) override
+    {
+        std::unique_lock<std::shared_mutex> lock(mutex_);
+        auto it = ledgers_.begin();
+        while (it != ledgers_.end() && it->first < ledgerSeq)
+        {
+            for (const auto& [txHash, _] : it->second.transactions)
+            {
+                transactionMap_.erase(txHash);
+            }
+            ledgerHashToSeq_.erase(it->second.info.hash);
+            it = ledgers_.erase(it);
+        }
+        for (auto& [_, accountData] : accountTxMap_)
+        {
+            auto txIt = accountData.ledgerTxMap.begin();
+            while (txIt != accountData.ledgerTxMap.end() &&
+                   txIt->first < ledgerSeq)
+            {
+                txIt = accountData.ledgerTxMap.erase(txIt);
+            }
+            accountData.transactions.erase(
+                std::remove_if(
+                    accountData.transactions.begin(),
+                    accountData.transactions.end(),
+                    [ledgerSeq](const AccountTx& tx) {
+                        return tx.second->getLgrSeq() < ledgerSeq;
+                    }),
+                accountData.transactions.end());
+        }
+    }
+
+    void
+    deleteTransactionsBeforeLedgerSeq(LedgerIndex ledgerSeq) override
+    {
+        std::unique_lock<std::shared_mutex> lock(mutex_);
+        for (auto& [seq, ledgerData] : ledgers_)
+        {
+            if (seq < ledgerSeq)
+            {
+                for (const auto& [txHash, _] : ledgerData.transactions)
+                {
+                    transactionMap_.erase(txHash);
+                }
+                ledgerData.transactions.clear();
+            }
+        }
+        for (auto& [_, accountData] : accountTxMap_)
+        {
+            auto txIt = accountData.ledgerTxMap.begin();
+            while (txIt != accountData.ledgerTxMap.end() &&
+                   txIt->first < ledgerSeq)
+            {
+                txIt = accountData.ledgerTxMap.erase(txIt);
+            }
+            accountData.transactions.erase(
+                std::remove_if(
+                    accountData.transactions.begin(),
+                    accountData.transactions.end(),
+                    [ledgerSeq](const AccountTx& tx) {
+                        return tx.second->getLgrSeq() < ledgerSeq;
+                    }),
+                accountData.transactions.end());
+        }
+    }
+
+    void
+    deleteAccountTransactionsBeforeLedgerSeq(LedgerIndex ledgerSeq) override
+    {
+        std::unique_lock<std::shared_mutex> lock(mutex_);
+        for (auto& [_, accountData] : accountTxMap_)
+        {
+            auto txIt = accountData.ledgerTxMap.begin();
+            while (txIt != accountData.ledgerTxMap.end() &&
+                   txIt->first < ledgerSeq)
+            {
+                txIt = accountData.ledgerTxMap.erase(txIt);
+            }
+            accountData.transactions.erase(
+                std::remove_if(
+                    accountData.transactions.begin(),
+                    accountData.transactions.end(),
+                    [ledgerSeq](const AccountTx& tx) {
+                        return tx.second->getLgrSeq() < ledgerSeq;
+                    }),
+                accountData.transactions.end());
+        }
+    }
+    std::size_t
+    getTransactionCount() override
+    {
+        std::shared_lock<std::shared_mutex> lock(mutex_);
+        return transactionMap_.size();
+    }
+
+    std::size_t
+    getAccountTransactionCount() override
+    {
+        std::shared_lock<std::shared_mutex> lock(mutex_);
+        std::size_t count = 0;
+        for (const auto& [_, accountData] : accountTxMap_)
+        {
+            count += accountData.transactions.size();
+        }
+        return count;
+    }
+
+    CountMinMax
+    getLedgerCountMinMax() override
+    {
+        std::shared_lock<std::shared_mutex> lock(mutex_);
+        if (ledgers_.empty())
+            return {0, 0, 0};
+        return {
+            ledgers_.size(), ledgers_.begin()->first, ledgers_.rbegin()->first};
+    }
+
+    bool
+    saveValidatedLedger(
+        std::shared_ptr<Ledger const> const& ledger,
+        bool current) override
+    {
+        std::unique_lock<std::shared_mutex> lock(mutex_);
+        LedgerData ledgerData;
+        ledgerData.info = ledger->info();
+        auto aLedger = std::make_shared<AcceptedLedger>(ledger, app_);
+
+        for (auto const& acceptedLedgerTx : *aLedger)
+        {
+            auto const& txn = acceptedLedgerTx->getTxn();
+            auto const& meta = acceptedLedgerTx->getMeta();
+            auto const& id = txn->getTransactionID();
+            std::string reason;
+
+            auto accTx = std::make_pair(
+                std::make_shared<ripple::Transaction>(txn, reason, app_),
+                std::make_shared<ripple::TxMeta>(meta));
+
+            ledgerData.transactions.emplace(id, accTx);
+            transactionMap_.emplace(id, accTx);
+
+            for (auto const& account : meta.getAffectedAccounts())
+            {
+                if (accountTxMap_.find(account) == accountTxMap_.end())
+                    accountTxMap_[account] = AccountTxData();
+                auto& accountData = accountTxMap_[account];
+                accountData.transactions.push_back(accTx);
+                accountData.ledgerTxMap[ledger->info().seq]
+                                       [acceptedLedgerTx->getTxnSeq()] =
+                    accountData.transactions.size() - 1;
+            }
+        }
+
+        ledgers_[ledger->info().seq] = std::move(ledgerData);
+        ledgerHashToSeq_[ledger->info().hash] = ledger->info().seq;
+
+        if (current)
+        {
+            auto const cutoffSeq =
+                ledger->info().seq > app_.config().LEDGER_HISTORY
+                ? ledger->info().seq - app_.config().LEDGER_HISTORY
+                : 0;
+
+            if (cutoffSeq > 0)
+            {
+                const std::size_t BATCH_SIZE = 128;
+                std::size_t deleted = 0;
+
+                std::vector<std::uint32_t> ledgersToDelete;
+                for (const auto& item : ledgers_)
+                {
+                    if (deleted >= BATCH_SIZE)
+                        break;
+                    if (item.first < cutoffSeq)
+                    {
+                        ledgersToDelete.push_back(item.first);
+                        deleted++;
+                    }
+                }
+
+                for (auto seq : ledgersToDelete)
+                {
+                    auto& ledgerToDelete = ledgers_[seq];
+
+                    for (const auto& txPair : ledgerToDelete.transactions)
+                    {
+                        transactionMap_.erase(txPair.first);
+                    }
+
+                    ledgerHashToSeq_.erase(ledgerToDelete.info.hash);
+                    ledgers_.erase(seq);
+                }
+
+                if (deleted > 0)
+                {
+                    for (auto& [account, data] : accountTxMap_)
+                    {
+                        auto it = data.ledgerTxMap.begin();
+                        while (it != data.ledgerTxMap.end())
+                        {
+                            if (it->first < cutoffSeq)
+                            {
+                                for (const auto& seqPair : it->second)
+                                {
+                                    if (seqPair.second <
+                                        data.transactions.size())
+                                    {
+                                        auto& txPair =
+                                            data.transactions[seqPair.second];
+                                        txPair.first.reset();
+                                        txPair.second.reset();
+                                    }
+                                }
+                                it = data.ledgerTxMap.erase(it);
+                            }
+                            else
+                            {
+                                ++it;
+                            }
+                        }
+
+                        data.transactions.erase(
+                            std::remove_if(
+                                data.transactions.begin(),
+                                data.transactions.end(),
+                                [](const auto& tx) {
+                                    return !tx.first && !tx.second;
+                                }),
+                            data.transactions.end());
+
+                        for (auto& [ledgerSeq, txMap] : data.ledgerTxMap)
+                        {
+                            for (auto& [txSeq, index] : txMap)
+                            {
+                                auto newIndex = std::distance(
+                                    data.transactions.begin(),
+                                    std::find(
+                                        data.transactions.begin(),
+                                        data.transactions.end(),
+                                        data.transactions[index]));
+                                index = newIndex;
+                            }
+                        }
+                    }
+
+                    app_.getLedgerMaster().clearPriorLedgers(cutoffSeq);
+                }
+            }
+        }
+
+        return true;
+    }
+
+    std::optional<LedgerInfo>
+    getLedgerInfoByIndex(LedgerIndex ledgerSeq) override
+    {
+        std::shared_lock<std::shared_mutex> lock(mutex_);
+        auto it = ledgers_.find(ledgerSeq);
+        if (it != ledgers_.end())
+            return it->second.info;
+        return std::nullopt;
+    }
+
+    std::optional<LedgerInfo>
+    getNewestLedgerInfo() override
+    {
+        std::shared_lock<std::shared_mutex> lock(mutex_);
+        if (ledgers_.empty())
+            return std::nullopt;
+        return ledgers_.rbegin()->second.info;
+    }
+
+    std::optional<LedgerInfo>
+    getLimitedOldestLedgerInfo(LedgerIndex ledgerFirstIndex) override
+    {
+        std::shared_lock<std::shared_mutex> lock(mutex_);
+        auto it = ledgers_.lower_bound(ledgerFirstIndex);
+        if (it != ledgers_.end())
+            return it->second.info;
+        return std::nullopt;
+    }
+
+    std::optional<LedgerInfo>
+    getLimitedNewestLedgerInfo(LedgerIndex ledgerFirstIndex) override
+    {
+        std::shared_lock<std::shared_mutex> lock(mutex_);
+        auto it = ledgers_.lower_bound(ledgerFirstIndex);
+        if (it == ledgers_.end())
+            return std::nullopt;
+        return ledgers_.rbegin()->second.info;
+    }
+
+    std::optional<LedgerInfo>
+    getLedgerInfoByHash(uint256 const& ledgerHash) override
+    {
+        std::shared_lock<std::shared_mutex> lock(mutex_);
+        auto it = ledgerHashToSeq_.find(ledgerHash);
+        if (it != ledgerHashToSeq_.end())
+            return ledgers_.at(it->second).info;
+        return std::nullopt;
+    }
+    uint256
+    getHashByIndex(LedgerIndex ledgerIndex) override
+    {
+        std::shared_lock<std::shared_mutex> lock(mutex_);
+        auto it = ledgers_.find(ledgerIndex);
+        if (it != ledgers_.end())
+            return it->second.info.hash;
+        return uint256();
+    }
+
+    std::optional<LedgerHashPair>
+    getHashesByIndex(LedgerIndex ledgerIndex) override
+    {
+        std::shared_lock<std::shared_mutex> lock(mutex_);
+        auto it = ledgers_.find(ledgerIndex);
+        if (it != ledgers_.end())
+        {
+            return LedgerHashPair{
+                it->second.info.hash, it->second.info.parentHash};
+        }
+        return std::nullopt;
+    }
+
+    std::map<LedgerIndex, LedgerHashPair>
+    getHashesByIndex(LedgerIndex minSeq, LedgerIndex maxSeq) override
+    {
+        std::shared_lock<std::shared_mutex> lock(mutex_);
+        std::map<LedgerIndex, LedgerHashPair> result;
+        auto it = ledgers_.lower_bound(minSeq);
+        auto end = ledgers_.upper_bound(maxSeq);
+        for (; it != end; ++it)
+        {
+            result[it->first] = LedgerHashPair{
+                it->second.info.hash, it->second.info.parentHash};
+        }
+        return result;
+    }
+
+    std::variant<AccountTx, TxSearched>
+    getTransaction(
+        uint256 const& id,
+        std::optional<ClosedInterval<std::uint32_t>> const& range,
+        error_code_i& ec) override
+    {
+        std::shared_lock<std::shared_mutex> lock(mutex_);
+        auto it = transactionMap_.find(id);
+        if (it != transactionMap_.end())
+        {
+            const auto& [txn, txMeta] = it->second;
+            if (!range ||
+                (range->lower() <= txMeta->getLgrSeq() &&
+                 txMeta->getLgrSeq() <= range->upper()))
+                return it->second;
+        }
+
+        if (range)
+        {
+            bool allPresent = true;
+            for (LedgerIndex seq = range->lower(); seq <= range->upper(); ++seq)
+            {
+                if (ledgers_.find(seq) == ledgers_.end())
+                {
+                    allPresent = false;
+                    break;
+                }
+            }
+            return allPresent ? TxSearched::all : TxSearched::some;
+        }
+
+        return TxSearched::unknown;
+    }
+
+    bool
+    ledgerDbHasSpace(Config const& config) override
+    {
+        return true;  // In-memory database always has space
+    }
+
+    bool
+    transactionDbHasSpace(Config const& config) override
+    {
+        return true;  // In-memory database always has space
+    }
+
+    std::uint32_t
+    getKBUsedAll() override
+    {
+        std::shared_lock<std::shared_mutex> lock(mutex_);
+        std::uint32_t size = sizeof(*this);
+        size += ledgers_.size() * (sizeof(LedgerIndex) + sizeof(LedgerData));
+        size +=
+            ledgerHashToSeq_.size() * (sizeof(uint256) + sizeof(LedgerIndex));
+        size += transactionMap_.size() * (sizeof(uint256) + sizeof(AccountTx));
+        for (const auto& [_, accountData] : accountTxMap_)
+        {
+            size += sizeof(AccountID) + sizeof(AccountTxData);
+            size += accountData.transactions.size() * sizeof(AccountTx);
+            for (const auto& [_, innerMap] : accountData.ledgerTxMap)
+            {
+                size += sizeof(uint32_t) +
+                    innerMap.size() * (sizeof(uint32_t) + sizeof(size_t));
+            }
+        }
+        return size / 1024;
+    }
+
+    std::uint32_t
+    getKBUsedLedger() override
+    {
+        std::shared_lock<std::shared_mutex> lock(mutex_);
+        std::uint32_t size = 0;
+        size += ledgers_.size() * (sizeof(LedgerIndex) + sizeof(LedgerData));
+        size +=
+            ledgerHashToSeq_.size() * (sizeof(uint256) + sizeof(LedgerIndex));
+        return size / 1024;
+    }
+
+    std::uint32_t
+    getKBUsedTransaction() override
+    {
+        std::shared_lock<std::shared_mutex> lock(mutex_);
+        std::uint32_t size = 0;
+        size += transactionMap_.size() * (sizeof(uint256) + sizeof(AccountTx));
+        for (const auto& [_, accountData] : accountTxMap_)
+        {
+            size += sizeof(AccountID) + sizeof(AccountTxData);
+            size += accountData.transactions.size() * sizeof(AccountTx);
+            for (const auto& [_, innerMap] : accountData.ledgerTxMap)
+            {
+                size += sizeof(uint32_t) +
+                    innerMap.size() * (sizeof(uint32_t) + sizeof(size_t));
+            }
+        }
+        return size / 1024;
+    }
+
+    void
+    closeLedgerDB() override
+    {
+        // No-op for in-memory database
+    }
+
+    void
+    closeTransactionDB() override
+    {
+        // No-op for in-memory database
+    }
+
+    ~RWDBDatabase()
+    {
+        // Regular maps can use standard clear
+        accountTxMap_.clear();
+        transactionMap_.clear();
+        for (auto& ledger : ledgers_)
+        {
+            ledger.second.transactions.clear();
+        }
+        ledgers_.clear();
+        ledgerHashToSeq_.clear();
+    }
+
+    std::vector<std::shared_ptr<Transaction>>
+    getTxHistory(LedgerIndex startIndex) override
+    {
+        std::shared_lock<std::shared_mutex> lock(mutex_);
+        std::vector<std::shared_ptr<Transaction>> result;
+        auto it = ledgers_.lower_bound(startIndex);
+        int count = 0;
+        while (it != ledgers_.end() && count < 20)
+        {
+            for (const auto& [txHash, accountTx] : it->second.transactions)
+            {
+                result.push_back(accountTx.first);
+                if (++count >= 20)
+                    break;
+            }
+            ++it;
+        }
+        return result;
+    }
+    // Helper function to handle limits
+    template <typename Container>
+    void
+    applyLimit(Container& container, std::size_t limit, bool bUnlimited)
+    {
+        if (!bUnlimited && limit > 0 && container.size() > limit)
+        {
+            container.resize(limit);
+        }
+    }
+
+    AccountTxs
+    getOldestAccountTxs(AccountTxOptions const& options) override
+    {
+        std::shared_lock<std::shared_mutex> lock(mutex_);
+        auto it = accountTxMap_.find(options.account);
+        if (it == accountTxMap_.end())
+            return {};
+
+        AccountTxs result;
+        const auto& accountData = it->second;
+        auto txIt = accountData.ledgerTxMap.lower_bound(options.minLedger);
+        auto txEnd = accountData.ledgerTxMap.upper_bound(options.maxLedger);
+
+        std::size_t skipped = 0;
+        for (; txIt != txEnd &&
+             (options.bUnlimited || result.size() < options.limit);
+             ++txIt)
+        {
+            for (const auto& [txSeq, txIndex] : txIt->second)
+            {
+                if (skipped < options.offset)
+                {
+                    ++skipped;
+                    continue;
+                }
+                result.push_back(accountData.transactions[txIndex]);
+                if (!options.bUnlimited && result.size() >= options.limit)
+                    break;
+            }
+        }
+
+        return result;
+    }
+
+    AccountTxs
+    getNewestAccountTxs(AccountTxOptions const& options) override
+    {
+        std::shared_lock<std::shared_mutex> lock(mutex_);
+        auto it = accountTxMap_.find(options.account);
+        if (it == accountTxMap_.end())
+            return {};
+
+        AccountTxs result;
+        const auto& accountData = it->second;
+        auto txIt = accountData.ledgerTxMap.lower_bound(options.minLedger);
+        auto txEnd = accountData.ledgerTxMap.upper_bound(options.maxLedger);
+
+        std::size_t skipped = 0;
+        for (auto rIt = std::make_reverse_iterator(txEnd);
+             rIt != std::make_reverse_iterator(txIt) &&
+             (options.bUnlimited || result.size() < options.limit);
+             ++rIt)
+        {
+            for (auto innerRIt = rIt->second.rbegin();
+                 innerRIt != rIt->second.rend();
+                 ++innerRIt)
+            {
+                if (skipped < options.offset)
+                {
+                    ++skipped;
+                    continue;
+                }
+                result.push_back(accountData.transactions[innerRIt->second]);
+                if (!options.bUnlimited && result.size() >= options.limit)
+                    break;
+            }
+        }
+
+        return result;
+    }
+
+    MetaTxsList
+    getOldestAccountTxsB(AccountTxOptions const& options) override
+    {
+        std::shared_lock<std::shared_mutex> lock(mutex_);
+        auto it = accountTxMap_.find(options.account);
+        if (it == accountTxMap_.end())
+            return {};
+
+        MetaTxsList result;
+        const auto& accountData = it->second;
+        auto txIt = accountData.ledgerTxMap.lower_bound(options.minLedger);
+        auto txEnd = accountData.ledgerTxMap.upper_bound(options.maxLedger);
+
+        std::size_t skipped = 0;
+        for (; txIt != txEnd &&
+             (options.bUnlimited || result.size() < options.limit);
+             ++txIt)
+        {
+            for (const auto& [txSeq, txIndex] : txIt->second)
+            {
+                if (skipped < options.offset)
+                {
+                    ++skipped;
+                    continue;
+                }
+                const auto& [txn, txMeta] = accountData.transactions[txIndex];
+                result.emplace_back(
+                    txn->getSTransaction()->getSerializer().peekData(),
+                    txMeta->getAsObject().getSerializer().peekData(),
+                    txIt->first);
+                if (!options.bUnlimited && result.size() >= options.limit)
+                    break;
+            }
+        }
+
+        return result;
+    }
+
+    MetaTxsList
+    getNewestAccountTxsB(AccountTxOptions const& options) override
+    {
+        std::shared_lock<std::shared_mutex> lock(mutex_);
+        auto it = accountTxMap_.find(options.account);
+        if (it == accountTxMap_.end())
+            return {};
+
+        MetaTxsList result;
+        const auto& accountData = it->second;
+        auto txIt = accountData.ledgerTxMap.lower_bound(options.minLedger);
+        auto txEnd = accountData.ledgerTxMap.upper_bound(options.maxLedger);
+
+        std::size_t skipped = 0;
+        for (auto rIt = std::make_reverse_iterator(txEnd);
+             rIt != std::make_reverse_iterator(txIt) &&
+             (options.bUnlimited || result.size() < options.limit);
+             ++rIt)
+        {
+            for (auto innerRIt = rIt->second.rbegin();
+                 innerRIt != rIt->second.rend();
+                 ++innerRIt)
+            {
+                if (skipped < options.offset)
+                {
+                    ++skipped;
+                    continue;
+                }
+                const auto& [txn, txMeta] =
+                    accountData.transactions[innerRIt->second];
+                result.emplace_back(
+                    txn->getSTransaction()->getSerializer().peekData(),
+                    txMeta->getAsObject().getSerializer().peekData(),
+                    rIt->first);
+                if (!options.bUnlimited && result.size() >= options.limit)
+                    break;
+            }
+        }
+
+        return result;
+    }
+    std::pair<AccountTxs, std::optional<AccountTxMarker>>
+    oldestAccountTxPage(AccountTxPageOptions const& options) override
+    {
+        std::shared_lock<std::shared_mutex> lock(mutex_);
+        auto it = accountTxMap_.find(options.account);
+        if (it == accountTxMap_.end())
+            return {{}, std::nullopt};
+
+        AccountTxs result;
+        std::optional<AccountTxMarker> marker;
+        const auto& accountData = it->second;
+        auto txIt = accountData.ledgerTxMap.lower_bound(options.minLedger);
+        auto txEnd = accountData.ledgerTxMap.upper_bound(options.maxLedger);
+
+        bool lookingForMarker = options.marker.has_value();
+        std::size_t count = 0;
+
+        for (; txIt != txEnd && (options.limit == 0 || count < options.limit);
+             ++txIt)
+        {
+            for (const auto& [txSeq, txIndex] : txIt->second)
+            {
+                if (lookingForMarker)
+                {
+                    if (txIt->first == options.marker->ledgerSeq &&
+                        txSeq == options.marker->txnSeq)
+                        lookingForMarker = false;
+                    continue;
+                }
+
+                result.push_back(accountData.transactions[txIndex]);
+                ++count;
+
+                if (options.limit > 0 && count >= options.limit)
+                {
+                    marker = AccountTxMarker{txIt->first, txSeq};
+                    break;
+                }
+            }
+        }
+
+        return {result, marker};
+    }
+
+    std::pair<AccountTxs, std::optional<AccountTxMarker>>
+    newestAccountTxPage(AccountTxPageOptions const& options) override
+    {
+        std::shared_lock<std::shared_mutex> lock(mutex_);
+        auto it = accountTxMap_.find(options.account);
+        if (it == accountTxMap_.end())
+            return {{}, std::nullopt};
+
+        AccountTxs result;
+        std::optional<AccountTxMarker> marker;
+        const auto& accountData = it->second;
+        auto txIt = accountData.ledgerTxMap.lower_bound(options.minLedger);
+        auto txEnd = accountData.ledgerTxMap.upper_bound(options.maxLedger);
+
+        bool lookingForMarker = options.marker.has_value();
+        std::size_t count = 0;
+
+        for (auto rIt = std::make_reverse_iterator(txEnd);
+             rIt != std::make_reverse_iterator(txIt) &&
+             (options.limit == 0 || count < options.limit);
+             ++rIt)
+        {
+            for (auto innerRIt = rIt->second.rbegin();
+                 innerRIt != rIt->second.rend();
+                 ++innerRIt)
+            {
+                if (lookingForMarker)
+                {
+                    if (rIt->first == options.marker->ledgerSeq &&
+                        innerRIt->first == options.marker->txnSeq)
+                        lookingForMarker = false;
+                    continue;
+                }
+
+                result.push_back(accountData.transactions[innerRIt->second]);
+                ++count;
+
+                if (options.limit > 0 && count >= options.limit)
+                {
+                    marker = AccountTxMarker{rIt->first, innerRIt->first};
+                    break;
+                }
+            }
+        }
+
+        return {result, marker};
+    }
+
+    std::pair<MetaTxsList, std::optional<AccountTxMarker>>
+    oldestAccountTxPageB(AccountTxPageOptions const& options) override
+    {
+        std::shared_lock<std::shared_mutex> lock(mutex_);
+        auto it = accountTxMap_.find(options.account);
+        if (it == accountTxMap_.end())
+            return {{}, std::nullopt};
+
+        MetaTxsList result;
+        std::optional<AccountTxMarker> marker;
+        const auto& accountData = it->second;
+        auto txIt = accountData.ledgerTxMap.lower_bound(options.minLedger);
+        auto txEnd = accountData.ledgerTxMap.upper_bound(options.maxLedger);
+
+        bool lookingForMarker = options.marker.has_value();
+        std::size_t count = 0;
+
+        for (; txIt != txEnd && (options.limit == 0 || count < options.limit);
+             ++txIt)
+        {
+            for (const auto& [txSeq, txIndex] : txIt->second)
+            {
+                if (lookingForMarker)
+                {
+                    if (txIt->first == options.marker->ledgerSeq &&
+                        txSeq == options.marker->txnSeq)
+                        lookingForMarker = false;
+                    continue;
+                }
+
+                const auto& [txn, txMeta] = accountData.transactions[txIndex];
+                result.emplace_back(
+                    txn->getSTransaction()->getSerializer().peekData(),
+                    txMeta->getAsObject().getSerializer().peekData(),
+                    txIt->first);
+                ++count;
+
+                if (options.limit > 0 && count >= options.limit)
+                {
+                    marker = AccountTxMarker{txIt->first, txSeq};
+                    break;
+                }
+            }
+        }
+
+        return {result, marker};
+    }
+
+    std::pair<MetaTxsList, std::optional<AccountTxMarker>>
+    newestAccountTxPageB(AccountTxPageOptions const& options) override
+    {
+        std::shared_lock<std::shared_mutex> lock(mutex_);
+        auto it = accountTxMap_.find(options.account);
+        if (it == accountTxMap_.end())
+            return {{}, std::nullopt};
+
+        MetaTxsList result;
+        std::optional<AccountTxMarker> marker;
+        const auto& accountData = it->second;
+        auto txIt = accountData.ledgerTxMap.lower_bound(options.minLedger);
+        auto txEnd = accountData.ledgerTxMap.upper_bound(options.maxLedger);
+
+        bool lookingForMarker = options.marker.has_value();
+        std::size_t count = 0;
+
+        for (auto rIt = std::make_reverse_iterator(txEnd);
+             rIt != std::make_reverse_iterator(txIt) &&
+             (options.limit == 0 || count < options.limit);
+             ++rIt)
+        {
+            for (auto innerRIt = rIt->second.rbegin();
+                 innerRIt != rIt->second.rend();
+                 ++innerRIt)
+            {
+                if (lookingForMarker)
+                {
+                    if (rIt->first == options.marker->ledgerSeq &&
+                        innerRIt->first == options.marker->txnSeq)
+                        lookingForMarker = false;
+                    continue;
+                }
+
+                const auto& [txn, txMeta] =
+                    accountData.transactions[innerRIt->second];
+                result.emplace_back(
+                    txn->getSTransaction()->getSerializer().peekData(),
+                    txMeta->getAsObject().getSerializer().peekData(),
+                    rIt->first);
+                ++count;
+
+                if (options.limit > 0 && count >= options.limit)
+                {
+                    marker = AccountTxMarker{rIt->first, innerRIt->first};
+                    break;
+                }
+            }
+        }
+
+        return {result, marker};
+    }
+};
+
+// Factory function
+std::unique_ptr<SQLiteDatabase>
+getRWDBDatabase(Application& app, Config const& config, JobQueue& jobQueue)
+{
+    return std::make_unique<RWDBDatabase>(app, config, jobQueue);
+}
+
+}  // namespace ripple
+#endif  // RIPPLE_APP_RDB_BACKEND_MEMORYDATABASE_H_INCLUDED

src/ripple/app/rdb/impl/RelationalDatabase.cpp

@@ -19,6 +19,8 @@
 
 #include <ripple/app/main/Application.h>
 #include <ripple/app/rdb/RelationalDatabase.h>
+#include <ripple/app/rdb/backend/FlatmapDatabase.h>
+#include <ripple/app/rdb/backend/RWDBDatabase.h>
 #include <ripple/core/ConfigSections.h>
 #include <ripple/nodestore/DatabaseShard.h>
 
@@ -38,6 +40,8 @@ RelationalDatabase::init(
 {
     bool use_sqlite = false;
     bool use_postgres = false;
+    bool use_rwdb = false;
+    bool use_flatmap = false;
 
     if (config.reporting())
     {
@@ -52,6 +56,14 @@ RelationalDatabase::init(
             {
                 use_sqlite = true;
             }
+            else if (boost::iequals(get(rdb_section, "backend"), "rwdb"))
+            {
+                use_rwdb = true;
+            }
+            else if (boost::iequals(get(rdb_section, "backend"), "flatmap"))
+            {
+                use_flatmap = true;
+            }
             else
             {
                 Throw<std::runtime_error>(
@@ -73,6 +85,14 @@ RelationalDatabase::init(
     {
         return getPostgresDatabase(app, config, jobQueue);
     }
+    else if (use_rwdb)
+    {
+        return getRWDBDatabase(app, config, jobQueue);
+    }
+    else if (use_flatmap)
+    {
+        return getFlatmapDatabase(app, config, jobQueue);
+    }
 
     return std::unique_ptr<RelationalDatabase>();
 }

src/ripple/core/Config.h

@@ -25,6 +25,7 @@
 #include <ripple/basics/base_uint.h>
 #include <ripple/beast/net/IPEndpoint.h>
 #include <ripple/beast/utility/Journal.h>
+#include <ripple/core/ConfigSections.h>
 #include <ripple/protocol/PublicKey.h>
 #include <ripple/protocol/SystemParameters.h>  // VFALCO Breaks levelization
 #include <boost/beast/core/string.hpp>
@@ -350,6 +351,21 @@ public:
     {
         return RUN_REPORTING;
     }
+    bool
+    mem_backend() const
+    {
+        static bool const isMem =
+            (!section(SECTION_RELATIONAL_DB).empty() &&
+             boost::beast::iequals(
+                 get(section(SECTION_RELATIONAL_DB), "backend"), "rwdb")) ||
+            (!section("node_db").empty() &&
+             (boost::beast::iequals(get(section("node_db"), "type"), "rwdb") ||
+              boost::beast::iequals(
+                  get(section("node_db"), "type"), "flatmap")));
+        // RHNOTE: memory type is not selected for here because it breaks
+        // tests
+        return isMem;
+    }
 
     bool
     useTxTables() const

src/ripple/nodestore/backend/FlatmapFactory.cpp

@@ -0,0 +1,235 @@
+#include <ripple/basics/contract.h>
+#include <ripple/nodestore/Factory.h>
+#include <ripple/nodestore/Manager.h>
+#include <ripple/nodestore/impl/DecodedBlob.h>
+#include <ripple/nodestore/impl/EncodedBlob.h>
+#include <ripple/nodestore/impl/codec.h>
+#include <boost/beast/core/string.hpp>
+#include <boost/core/ignore_unused.hpp>
+#include <boost/unordered/concurrent_flat_map.hpp>
+#include <memory>
+#include <mutex>
+
+namespace ripple {
+namespace NodeStore {
+
+class FlatmapBackend : public Backend
+{
+private:
+    std::string name_;
+    beast::Journal journal_;
+    bool isOpen_{false};
+
+    struct base_uint_hasher
+    {
+        using result_type = std::size_t;
+
+        result_type
+        operator()(base_uint<256> const& value) const
+        {
+            return hardened_hash<>{}(value);
+        }
+    };
+
+    using DataStore = boost::unordered::concurrent_flat_map<
+        uint256,
+        std::vector<std::uint8_t>,  // Store compressed blob data
+        base_uint_hasher>;
+
+    DataStore table_;
+
+public:
+    FlatmapBackend(
+        size_t keyBytes,
+        Section const& keyValues,
+        beast::Journal journal)
+        : name_(get(keyValues, "path")), journal_(journal)
+    {
+        boost::ignore_unused(journal_);
+        if (name_.empty())
+            name_ = "node_db";
+    }
+
+    ~FlatmapBackend() override
+    {
+        close();
+    }
+
+    std::string
+    getName() override
+    {
+        return name_;
+    }
+
+    void
+    open(bool createIfMissing) override
+    {
+        if (isOpen_)
+            Throw<std::runtime_error>("already open");
+        isOpen_ = true;
+    }
+
+    bool
+    isOpen() override
+    {
+        return isOpen_;
+    }
+
+    void
+    close() override
+    {
+        table_.clear();
+        isOpen_ = false;
+    }
+
+    Status
+    fetch(void const* key, std::shared_ptr<NodeObject>* pObject) override
+    {
+        if (!isOpen_)
+            return notFound;
+
+        uint256 const hash(uint256::fromVoid(key));
+
+        bool found = table_.visit(hash, [&](const auto& key_value_pair) {
+            nudb::detail::buffer bf;
+            auto const result = nodeobject_decompress(
+                key_value_pair.second.data(), key_value_pair.second.size(), bf);
+            DecodedBlob decoded(hash.data(), result.first, result.second);
+            if (!decoded.wasOk())
+            {
+                *pObject = nullptr;
+                return;
+            }
+            *pObject = decoded.createObject();
+        });
+        return found ? (*pObject ? ok : dataCorrupt) : notFound;
+    }
+
+    std::pair<std::vector<std::shared_ptr<NodeObject>>, Status>
+    fetchBatch(std::vector<uint256 const*> const& hashes) override
+    {
+        std::vector<std::shared_ptr<NodeObject>> results;
+        results.reserve(hashes.size());
+        for (auto const& h : hashes)
+        {
+            std::shared_ptr<NodeObject> nObj;
+            Status status = fetch(h->begin(), &nObj);
+            if (status != ok)
+                results.push_back({});
+            else
+                results.push_back(nObj);
+        }
+        return {results, ok};
+    }
+
+    void
+    store(std::shared_ptr<NodeObject> const& object) override
+    {
+        if (!isOpen_)
+            return;
+
+        if (!object)
+            return;
+
+        EncodedBlob encoded(object);
+        nudb::detail::buffer bf;
+        auto const result =
+            nodeobject_compress(encoded.getData(), encoded.getSize(), bf);
+
+        std::vector<std::uint8_t> compressed(
+            static_cast<const std::uint8_t*>(result.first),
+            static_cast<const std::uint8_t*>(result.first) + result.second);
+
+        table_.insert_or_assign(object->getHash(), std::move(compressed));
+    }
+
+    void
+    storeBatch(Batch const& batch) override
+    {
+        for (auto const& e : batch)
+            store(e);
+    }
+
+    void
+    sync() override
+    {
+    }
+
+    void
+    for_each(std::function<void(std::shared_ptr<NodeObject>)> f) override
+    {
+        if (!isOpen_)
+            return;
+
+        table_.visit_all([&f](const auto& entry) {
+            nudb::detail::buffer bf;
+            auto const result = nodeobject_decompress(
+                entry.second.data(), entry.second.size(), bf);
+            DecodedBlob decoded(
+                entry.first.data(), result.first, result.second);
+            if (decoded.wasOk())
+                f(decoded.createObject());
+        });
+    }
+
+    int
+    getWriteLoad() override
+    {
+        return 0;
+    }
+
+    void
+    setDeletePath() override
+    {
+        close();
+    }
+
+    int
+    fdRequired() const override
+    {
+        return 0;
+    }
+
+private:
+    size_t
+    size() const
+    {
+        return table_.size();
+    }
+};
+
+class FlatmapFactory : public Factory
+{
+public:
+    FlatmapFactory()
+    {
+        Manager::instance().insert(*this);
+    }
+
+    ~FlatmapFactory() override
+    {
+        Manager::instance().erase(*this);
+    }
+
+    std::string
+    getName() const override
+    {
+        return "Flatmap";
+    }
+
+    std::unique_ptr<Backend>
+    createInstance(
+        size_t keyBytes,
+        Section const& keyValues,
+        std::size_t burstSize,
+        Scheduler& scheduler,
+        beast::Journal journal) override
+    {
+        return std::make_unique<FlatmapBackend>(keyBytes, keyValues, journal);
+    }
+};
+
+static FlatmapFactory flatmapFactory;
+
+}  // namespace NodeStore
+}  // namespace ripple

src/ripple/nodestore/backend/MemoryFactory.cpp

@@ -94,7 +94,7 @@ public:
     {
         boost::ignore_unused(journal_);  // Keep unused journal_ just in case.
         if (name_.empty())
-            Throw<std::runtime_error>("Missing path in Memory backend");
+            Throw<std::runtime_error>("Missing path in TestMemory backend");
     }
 
     ~MemoryBackend() override

src/ripple/nodestore/backend/RWDBFactory.cpp

@@ -0,0 +1,242 @@
+#include <ripple/basics/contract.h>
+#include <ripple/nodestore/Factory.h>
+#include <ripple/nodestore/Manager.h>
+#include <ripple/nodestore/impl/DecodedBlob.h>
+#include <ripple/nodestore/impl/EncodedBlob.h>
+#include <ripple/nodestore/impl/codec.h>
+#include <boost/beast/core/string.hpp>
+#include <boost/core/ignore_unused.hpp>
+#include <boost/unordered/concurrent_flat_map.hpp>
+#include <memory>
+#include <mutex>
+
+namespace ripple {
+namespace NodeStore {
+
+class RWDBBackend : public Backend
+{
+private:
+    std::string name_;
+    beast::Journal journal_;
+    bool isOpen_{false};
+
+    struct base_uint_hasher
+    {
+        using result_type = std::size_t;
+
+        result_type
+        operator()(base_uint<256> const& value) const
+        {
+            return hardened_hash<>{}(value);
+        }
+    };
+
+    using DataStore =
+        std::map<uint256, std::vector<std::uint8_t>>;  // Store compressed blob
+                                                       // data
+    mutable std::recursive_mutex
+        mutex_;  // Only needed for std::map implementation
+
+    DataStore table_;
+
+public:
+    RWDBBackend(
+        size_t keyBytes,
+        Section const& keyValues,
+        beast::Journal journal)
+        : name_(get(keyValues, "path")), journal_(journal)
+    {
+        boost::ignore_unused(journal_);
+        if (name_.empty())
+            name_ = "node_db";
+    }
+
+    ~RWDBBackend() override
+    {
+        close();
+    }
+
+    std::string
+    getName() override
+    {
+        return name_;
+    }
+
+    void
+    open(bool createIfMissing) override
+    {
+        std::lock_guard lock(mutex_);
+        if (isOpen_)
+            Throw<std::runtime_error>("already open");
+        isOpen_ = true;
+    }
+
+    bool
+    isOpen() override
+    {
+        return isOpen_;
+    }
+
+    void
+    close() override
+    {
+        std::lock_guard lock(mutex_);
+        table_.clear();
+        isOpen_ = false;
+    }
+
+    Status
+    fetch(void const* key, std::shared_ptr<NodeObject>* pObject) override
+    {
+        if (!isOpen_)
+            return notFound;
+
+        uint256 const hash(uint256::fromVoid(key));
+
+        std::lock_guard lock(mutex_);
+        auto it = table_.find(hash);
+        if (it == table_.end())
+            return notFound;
+
+        nudb::detail::buffer bf;
+        auto const result =
+            nodeobject_decompress(it->second.data(), it->second.size(), bf);
+        DecodedBlob decoded(hash.data(), result.first, result.second);
+        if (!decoded.wasOk())
+            return dataCorrupt;
+        *pObject = decoded.createObject();
+        return ok;
+    }
+
+    std::pair<std::vector<std::shared_ptr<NodeObject>>, Status>
+    fetchBatch(std::vector<uint256 const*> const& hashes) override
+    {
+        std::vector<std::shared_ptr<NodeObject>> results;
+        results.reserve(hashes.size());
+        for (auto const& h : hashes)
+        {
+            std::shared_ptr<NodeObject> nObj;
+            Status status = fetch(h->begin(), &nObj);
+            if (status != ok)
+                results.push_back({});
+            else
+                results.push_back(nObj);
+        }
+        return {results, ok};
+    }
+
+    void
+    store(std::shared_ptr<NodeObject> const& object) override
+    {
+        if (!isOpen_)
+            return;
+
+        if (!object)
+            return;
+
+        EncodedBlob encoded(object);
+        nudb::detail::buffer bf;
+        auto const result =
+            nodeobject_compress(encoded.getData(), encoded.getSize(), bf);
+
+        std::vector<std::uint8_t> compressed(
+            static_cast<const std::uint8_t*>(result.first),
+            static_cast<const std::uint8_t*>(result.first) + result.second);
+
+        std::lock_guard lock(mutex_);
+        table_[object->getHash()] = std::move(compressed);
+    }
+
+    void
+    storeBatch(Batch const& batch) override
+    {
+        for (auto const& e : batch)
+            store(e);
+    }
+
+    void
+    sync() override
+    {
+    }
+
+    void
+    for_each(std::function<void(std::shared_ptr<NodeObject>)> f) override
+    {
+        if (!isOpen_)
+            return;
+
+        std::lock_guard lock(mutex_);
+        for (const auto& entry : table_)
+        {
+            nudb::detail::buffer bf;
+            auto const result = nodeobject_decompress(
+                entry.second.data(), entry.second.size(), bf);
+            DecodedBlob decoded(
+                entry.first.data(), result.first, result.second);
+            if (decoded.wasOk())
+                f(decoded.createObject());
+        }
+    }
+
+    int
+    getWriteLoad() override
+    {
+        return 0;
+    }
+
+    void
+    setDeletePath() override
+    {
+        close();
+    }
+
+    int
+    fdRequired() const override
+    {
+        return 0;
+    }
+
+private:
+    size_t
+    size() const
+    {
+        std::lock_guard lock(mutex_);
+        return table_.size();
+    }
+};
+
+class RWDBFactory : public Factory
+{
+public:
+    RWDBFactory()
+    {
+        Manager::instance().insert(*this);
+    }
+
+    ~RWDBFactory() override
+    {
+        Manager::instance().erase(*this);
+    }
+
+    std::string
+    getName() const override
+    {
+        return "RWDB";
+    }
+
+    std::unique_ptr<Backend>
+    createInstance(
+        size_t keyBytes,
+        Section const& keyValues,
+        std::size_t burstSize,
+        Scheduler& scheduler,
+        beast::Journal journal) override
+    {
+        return std::make_unique<RWDBBackend>(keyBytes, keyValues, journal);
+    }
+};
+
+static RWDBFactory rwDBFactory;
+
+}  // namespace NodeStore
+}  // namespace ripple

src/ripple/overlay/impl/OverlayImpl.cpp

@@ -38,6 +38,7 @@
 #include <ripple/rpc/json_body.h>
 #include <ripple/server/SimpleWriter.h>
 
+#include <ripple/core/ConfigSections.h>
 #include <boost/algorithm/string/predicate.hpp>
 #include <boost/utility/in_place_factory.hpp>
 
@@ -136,7 +137,11 @@ OverlayImpl::OverlayImpl(
           stopwatch(),
           app_.journal("PeerFinder"),
           config,
-          collector))
+          collector,
+          app.config().section(SECTION_RELATIONAL_DB).empty() ||
+              !boost::iequals(
+                  get(app.config().section(SECTION_RELATIONAL_DB), "backend"),
+                  "rwdb")))
     , m_resolver(resolver)
     , next_id_(1)
     , timer_count_(0)

src/ripple/peerfinder/impl/InMemoryStore.h

@@ -0,0 +1,54 @@
+#ifndef RIPPLE_PEERFINDER_INMEMORYSTORE_H_INCLUDED
+#define RIPPLE_PEERFINDER_INMEMORYSTORE_H_INCLUDED
+
+#include <ripple/beast/net/IPEndpoint.h>
+#include <ripple/peerfinder/impl/Store.h>
+#include <boost/functional/hash.hpp>
+#include <boost/unordered/concurrent_flat_map.hpp>
+
+namespace ripple {
+namespace PeerFinder {
+
+struct EndpointHasher
+{
+    std::size_t
+    operator()(beast::IP::Endpoint const& endpoint) const
+    {
+        std::size_t seed = 0;
+        boost::hash_combine(seed, endpoint.address().to_string());
+        boost::hash_combine(seed, endpoint.port());
+        return seed;
+    }
+};
+
+class InMemoryStore : public Store
+{
+private:
+    boost::concurrent_flat_map<beast::IP::Endpoint, int, EndpointHasher>
+        entries;
+
+public:
+    std::size_t
+    load(load_callback const& cb) override
+    {
+        std::size_t count = 0;
+        entries.visit_all([&](auto const& entry) {
+            cb(entry.first, entry.second);
+            ++count;
+        });
+        return count;
+    }
+
+    void
+    save(std::vector<Entry> const& v) override
+    {
+        entries.clear();
+        for (auto const& entry : v)
+            entries.emplace(entry.endpoint, entry.valence);
+    }
+};
+
+}  // namespace PeerFinder
+}  // namespace ripple
+
+#endif

src/ripple/peerfinder/impl/PeerfinderManager.cpp

@@ -17,8 +17,10 @@
 */
 //==============================================================================
 
+#include <ripple/core/ConfigSections.h>
 #include <ripple/peerfinder/PeerfinderManager.h>
 #include <ripple/peerfinder/impl/Checker.h>
+#include <ripple/peerfinder/impl/InMemoryStore.h>
 #include <ripple/peerfinder/impl/Logic.h>
 #include <ripple/peerfinder/impl/SourceStrings.h>
 #include <ripple/peerfinder/impl/StoreSqdb.h>
@@ -38,7 +40,7 @@ public:
     std::optional<boost::asio::io_service::work> work_;
     clock_type& m_clock;
     beast::Journal m_journal;
-    StoreSqdb m_store;
+    std::unique_ptr<Store> m_store;
     Checker<boost::asio::ip::tcp> checker_;
     Logic<decltype(checker_)> m_logic;
     BasicConfig const& m_config;
@@ -50,15 +52,18 @@ public:
         clock_type& clock,
         beast::Journal journal,
         BasicConfig const& config,
-        beast::insight::Collector::ptr const& collector)
+        beast::insight::Collector::ptr const& collector,
+        bool useSqLiteStore)
         : Manager()
         , io_service_(io_service)
         , work_(std::in_place, std::ref(io_service_))
         , m_clock(clock)
         , m_journal(journal)
-        , m_store(journal)
+        , m_store(
+              useSqLiteStore ? static_cast<Store*>(new StoreSqdb(journal))
+                             : static_cast<Store*>(new InMemoryStore()))
         , checker_(io_service_)
-        , m_logic(clock, m_store, checker_, journal)
+        , m_logic(clock, *m_store, checker_, journal)
         , m_config(config)
         , m_stats(std::bind(&ManagerImp::collect_metrics, this), collector)
     {
@@ -215,7 +220,8 @@ public:
     void
     start() override
     {
-        m_store.open(m_config);
+        if (auto sqdb = dynamic_cast<StoreSqdb*>(m_store.get()))
+            sqdb->open(m_config);
         m_logic.load();
     }
 
@@ -275,10 +281,11 @@ make_Manager(
     clock_type& clock,
     beast::Journal journal,
     BasicConfig const& config,
-    beast::insight::Collector::ptr const& collector)
+    beast::insight::Collector::ptr const& collector,
+    bool useSqLiteStore)
 {
     return std::make_unique<ManagerImp>(
-        io_service, clock, journal, config, collector);
+        io_service, clock, journal, config, collector, useSqLiteStore);
 }
 
 }  // namespace PeerFinder

src/ripple/peerfinder/make_Manager.h

@@ -34,7 +34,8 @@ make_Manager(
     clock_type& clock,
     beast::Journal journal,
     BasicConfig const& config,
-    beast::insight::Collector::ptr const& collector);
+    beast::insight::Collector::ptr const& collector,
+    bool useSqliteStore);
 
 }  // namespace PeerFinder
 }  // namespace ripple

src/ripple/shamap/impl/SHAMap.cpp

@@ -244,6 +244,7 @@ SHAMap::checkFilter(SHAMapHash const& hash, SHAMapSyncFilter* filter) const
 
 // Get a node without throwing
 // Used on maps where missing nodes are expected
+/*
 std::shared_ptr<SHAMapTreeNode>
 SHAMap::fetchNodeNT(SHAMapHash const& hash, SHAMapSyncFilter* filter) const
 {
@@ -266,6 +267,49 @@ SHAMap::fetchNodeNT(SHAMapHash const& hash, SHAMapSyncFilter* filter) const
 
     return node;
 }
+*/
+
+std::shared_ptr<SHAMapTreeNode>
+SHAMap::fetchNodeNT(SHAMapHash const& hash, SHAMapSyncFilter* filter) const
+{
+    using namespace std::chrono;
+    auto start = high_resolution_clock::now();
+    auto timeout = nanoseconds(50);
+
+    while (true)
+    {
+        // Try to fetch from cache first
+        auto node = cacheLookup(hash);
+        if (node)
+            return node;
+
+        if (backed_)
+        {
+            node = fetchNodeFromDB(hash);
+            if (node)
+            {
+                canonicalize(hash, node);
+                return node;
+            }
+        }
+
+        if (filter)
+            node = checkFilter(hash, filter);
+
+        if (node)
+            return node;
+
+        // Check if we've exceeded timeout
+        auto elapsed = high_resolution_clock::now() - start;
+        if (elapsed >= timeout)
+            break;
+
+        // Short yield to avoid overwhelming CPU
+        std::this_thread::yield();
+    }
+
+    return nullptr;
+}
 
 std::shared_ptr<SHAMapTreeNode>
 SHAMap::fetchNodeNT(SHAMapHash const& hash) const

src/test/nodestore/Backend_test.cpp

@@ -82,6 +82,8 @@ public:
             }
         }
 
+        // rwdb backend does not keep table/data after close
+        if (type != "rwdb")
         {
             // Re-open the backend
             std::unique_ptr<Backend> backend = Manager::instance().make_Backend(
@@ -105,6 +107,8 @@ public:
     {
         std::uint64_t const seedValue = 50;
 
+        testBackend("memory", seedValue);
+        testBackend("rwdb", seedValue);
         testBackend("nudb", seedValue);
 
 #if RIPPLE_ROCKSDB_AVAILABLE
@@ -117,7 +121,7 @@ public:
     }
 };
 
-BEAST_DEFINE_TESTSUITE(Backend, ripple_core, ripple);
+BEAST_DEFINE_TESTSUITE(Backend, NodeStore, ripple);
 
 }  // namespace NodeStore
 }  // namespace ripple

src/test/nodestore/Database_test.cpp

@@ -661,6 +661,8 @@ public:
 
         testNodeStore("memory", false, seedValue);
 
+        testNodeStore("rwdb", false, seedValue);
+
         // Persistent backend tests
         {
             testNodeStore("nudb", true, seedValue);