From ed5809502942acdfd91bcfadcd733234ded76d39 Mon Sep 17 00:00:00 2001
From: Nathan Nichols <natenichols@cox.net>
Date: Fri, 14 May 2021 09:45:31 -0500
Subject: [PATCH] add a limit

---
 reporting/CassandraBackend.cpp | 12 +++++++++---
 reporting/PostgresBackend.cpp  |  8 ++++++--
 2 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/reporting/CassandraBackend.cpp b/reporting/CassandraBackend.cpp
index 59a34146..e4f79e37 100644
--- a/reporting/CassandraBackend.cpp
+++ b/reporting/CassandraBackend.cpp
@@ -502,12 +502,15 @@ CassandraBackend::fetchBookOffers(
     std::optional<ripple::uint256> const& cursor) const
 {
     auto rng = fetchLedgerRange();
+    auto limitTuningFactor = 50;
     
     if(!rng)
         return {{},{}};
 
-    auto readBooks = [this, &book](std::uint32_t sequence) 
-            -> std::pair<bool, std::vector<std::pair<std::uint64_t, ripple::uint256>>>
+    auto readBooks = 
+        [this, &book, &limit, &limitTuningFactor]
+        (std::uint32_t sequence) 
+        -> std::pair<bool, std::vector<std::pair<std::uint64_t, ripple::uint256>>>
     {
         CassandraStatement completeQuery{completeBook_};
         completeQuery.bindInt(sequence);
@@ -527,6 +530,8 @@ CassandraBackend::fetchBookOffers(
         statement.bindBytes(zero.data(), 8);
         statement.bindBytes(zero);
 
+        statement.bindUInt(limit * limitTuningFactor);
+
         auto start = std::chrono::system_clock::now();
 
         CassandraResult result = executeSyncRead(statement);
@@ -1550,7 +1555,8 @@ CassandraBackend::open(bool readOnly)
         query << "SELECT quality_key FROM " << tablePrefix << "books "
               << " WHERE book = ? AND sequence = ?"
               << " AND quality_key >= (?, ?)"
-                 " ORDER BY quality_key ASC";
+                 " ORDER BY quality_key ASC "
+                 " LIMIT ?";
         if (!selectBook_.prepareStatement(query, session_.get()))
             continue;
 
diff --git a/reporting/PostgresBackend.cpp b/reporting/PostgresBackend.cpp
index 6cdd818f..d97c7d80 100644
--- a/reporting/PostgresBackend.cpp
+++ b/reporting/PostgresBackend.cpp
@@ -379,6 +379,7 @@ PostgresBackend::fetchBookOffers(
     std::optional<ripple::uint256> const& cursor) const
 {
     auto rng = fetchLedgerRange();
+    auto limitTuningFactor = 50;
 
     if(!rng)
         return {{},{}};
@@ -388,7 +389,9 @@ PostgresBackend::fetchBookOffers(
     ripple::uint256 bookEnd = ripple::getQualityNext(bookBase);
 
     using bookKeyPair = std::pair<ripple::uint256, ripple::uint256>;
-    auto getBooks = [this, &bookBase, &bookEnd, &limit](std::uint32_t sequence)
+    auto getBooks = 
+        [this, &bookBase, &bookEnd, &limit, &limitTuningFactor]
+        (std::uint32_t sequence)
         -> std::pair<bool, std::vector<bookKeyPair>>
     {
         BOOST_LOG_TRIVIAL(info) << __func__ << ": Fetching books between "
@@ -418,7 +421,8 @@ PostgresBackend::fetchBookOffers(
             << "\'\\x" << ripple::strHex(bookBase) << "\' "
             << "AND book < "
             << "\'\\x" << ripple::strHex(bookEnd) << "\' "
-            << "ORDER BY book ASC";
+            << "ORDER BY book ASC "
+            << "LIMIT " << std::to_string(limit * limitTuningFactor);
 
         BOOST_LOG_TRIVIAL(debug) << sql.str();