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Database read throttle (#242)

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Track current outstanding read requests to the database. When the configured limit is exceeded, reject new RPCs and return rpcTOO_BUSY
This commit is contained in:
CJ Cobb
2022-09-23 15:43:03 -05:00
committed by GitHub
parent 1764f3524e
commit eb1ea28e27
7 changed files with 113 additions and 70 deletions
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3
example-config.json
View File

@@ -9,7 +9,8 @@
"keyspace":"clio",
"replication_factor":1,
"table_prefix":"",
"max_requests_outstanding":25000,
"max_write_requests_outstanding":25000,
"max_read_requests_outstanding":30000,
"threads":8
}
},

10
src/backend/BackendInterface.h
View File

@@ -7,10 +7,12 @@
#include <backend/Types.h>
#include <thread>
#include <type_traits>
namespace Backend {
class DatabaseTimeout : public std::exception
{
public:
const char*
what() const throw() override
{
@@ -30,9 +32,10 @@ retryOnTimeout(F func, size_t waitMs = 500)
}
catch (DatabaseTimeout& t)
{
std::this_thread::sleep_for(std::chrono::milliseconds(waitMs));
BOOST_LOG_TRIVIAL(error)
<< __func__ << " function timed out. Retrying ... ";
<< __func__
<< " Database request timed out. Sleeping and retrying ... ";
std::this_thread::sleep_for(std::chrono::milliseconds(waitMs));
}
}
}
@@ -342,6 +345,9 @@ public:
virtual void
close(){};
virtual bool
isTooBusy() const = 0;
// *** private helper methods
private:
virtual void

26
src/backend/CassandraBackend.cpp
View File

@@ -486,6 +486,7 @@ CassandraBackend::fetchTransactions(
{
if (hashes.size() == 0)
return {};
numReadRequestsOutstanding_ += hashes.size();
handler_type handler(std::forward<decltype(yield)>(yield));
result_type result(handler);
@@ -518,6 +519,7 @@ CassandraBackend::fetchTransactions(
// suspend the coroutine until completion handler is called.
result.get();
numReadRequestsOutstanding_ -= hashes.size();
auto end = std::chrono::system_clock::now();
for (auto const& cb : cbs)
@@ -812,6 +814,8 @@ CassandraBackend::doFetchLedgerObjects(
if (keys.size() == 0)
return {};
numReadRequestsOutstanding_ += keys.size();
handler_type handler(std::forward<decltype(yield)>(yield));
result_type result(handler);
@@ -838,6 +842,7 @@ CassandraBackend::doFetchLedgerObjects(
// suspend the coroutine until completion handler is called.
result.get();
numReadRequestsOutstanding_ -= keys.size();
for (auto const& cb : cbs)
{
@@ -965,6 +970,12 @@ CassandraBackend::doOnlineDelete(
return true;
}
bool
CassandraBackend::isTooBusy() const
{
return numReadRequestsOutstanding_ >= maxReadRequestsOutstanding;
}
void
CassandraBackend::open(bool readOnly)
{
@@ -1077,21 +1088,26 @@ CassandraBackend::open(bool readOnly)
<< ", result: " << rc << ", " << cass_error_desc(rc);
throw std::runtime_error(ss.str());
}
if (getInt("max_requests_outstanding"))
maxRequestsOutstanding = *getInt("max_requests_outstanding");
if (getInt("max_write_requests_outstanding"))
maxWriteRequestsOutstanding = *getInt("max_write_requests_outstanding");
if (getInt("max_read_requests_outstanding"))
maxReadRequestsOutstanding = *getInt("max_read_requests_outstanding");
if (getInt("sync_interval"))
syncInterval_ = *getInt("sync_interval");
BOOST_LOG_TRIVIAL(info)
<< __func__ << " sync interval is " << syncInterval_
<< ". max requests outstanding is " << maxRequestsOutstanding;
<< ". max write requests outstanding is " << maxWriteRequestsOutstanding
<< ". max read requests outstanding is " << maxReadRequestsOutstanding;
cass_cluster_set_request_timeout(cluster, 10000);
rc = cass_cluster_set_queue_size_io(
cluster,
maxRequestsOutstanding); // This number needs to scale w/ the
// number of request per sec
maxWriteRequestsOutstanding +
maxReadRequestsOutstanding); // This number needs to scale w/ the
// number of request per sec
if (rc != CASS_OK)
{
std::stringstream ss;

30
src/backend/CassandraBackend.h
View File

@@ -645,13 +645,18 @@ private:
uint32_t syncInterval_ = 1;
uint32_t lastSync_ = 0;
// maximum number of concurrent in flight requests. New requests will wait
// for earlier requests to finish if this limit is exceeded
std::uint32_t maxRequestsOutstanding = 10000;
mutable std::atomic_uint32_t numRequestsOutstanding_ = 0;
// maximum number of concurrent in flight write requests. New requests will
// wait for earlier requests to finish if this limit is exceeded
std::uint32_t maxWriteRequestsOutstanding = 10000;
mutable std::atomic_uint32_t numWriteRequestsOutstanding_ = 0;
// maximum number of concurrent in flight read requests. isTooBusy() will
// return true if the number of in flight read requests exceeds this limit
std::uint32_t maxReadRequestsOutstanding = 100000;
mutable std::atomic_uint32_t numReadRequestsOutstanding_ = 0;
// mutex and condition_variable to limit the number of concurrent in flight
// requests
// write requests
mutable std::mutex throttleMutex_;
mutable std::condition_variable throttleCv_;
@@ -1017,6 +1022,9 @@ public:
std::uint32_t const numLedgersToKeep,
boost::asio::yield_context& yield) const override;
bool
isTooBusy() const override;
inline void
incremementOutstandingRequestCount() const
{
@@ -1031,19 +1039,19 @@ public:
throttleCv_.wait(lck, [this]() { return canAddRequest(); });
}
}
++numRequestsOutstanding_;
++numWriteRequestsOutstanding_;
}
inline void
decrementOutstandingRequestCount() const
{
// sanity check
if (numRequestsOutstanding_ == 0)
if (numWriteRequestsOutstanding_ == 0)
{
assert(false);
throw std::runtime_error("decrementing num outstanding below 0");
}
size_t cur = (--numRequestsOutstanding_);
size_t cur = (--numWriteRequestsOutstanding_);
{
// mutex lock required to prevent race condition around spurious
// wakeup
@@ -1062,13 +1070,13 @@ public:
inline bool
canAddRequest() const
{
return numRequestsOutstanding_ < maxRequestsOutstanding;
return numWriteRequestsOutstanding_ < maxWriteRequestsOutstanding;
}
inline bool
finishedAllRequests() const
{
return numRequestsOutstanding_ == 0;
return numWriteRequestsOutstanding_ == 0;
}
void
@@ -1209,10 +1217,12 @@ public:
CassError rc;
do
{
++numReadRequestsOutstanding_;
fut = cass_session_execute(session_.get(), statement.get());
boost::system::error_code ec;
rc = cass_future_error_code(fut, yield[ec]);
--numReadRequestsOutstanding_;
if (ec)
{

6
src/backend/PostgresBackend.h
View File

@@ -156,6 +156,12 @@ public:
bool
doFinishWrites() override;
bool
isTooBusy() const override
{
return false;
}
bool
doOnlineDelete(
std::uint32_t const numLedgersToKeep,

12
src/rpc/RPC.cpp
View File

@@ -342,6 +342,13 @@ buildResponse(Context const& ctx)
if (ctx.method == "ping")
return boost::json::object{};
if (ctx.backend->isTooBusy())
{
BOOST_LOG_TRIVIAL(error)
<< __func__ << " Database is too busy. Rejecting request";
return Status{Error::rpcTOO_BUSY};
}
auto method = handlerTable.getHandler(ctx.method);
if (!method)
@@ -364,6 +371,11 @@ buildResponse(Context const& ctx)
{
return Status{Error::rpcACT_NOT_FOUND, err.what()};
}
catch (Backend::DatabaseTimeout const& t)
{
BOOST_LOG_TRIVIAL(error) << __func__ << " Database timeout";
return Status{Error::rpcTOO_BUSY};
}
catch (std::exception const& err)
{
BOOST_LOG_TRIVIAL(error)

96
src/webserver/WsBase.h
View File

@@ -266,59 +266,51 @@ public:
try
{
BOOST_LOG_TRIVIAL(debug) << " received request : " << request;
try
{
auto range = backend_->fetchLedgerRange();
if (!range)
return sendError(RPC::Error::rpcNOT_READY);
std::optional<RPC::Context> context = RPC::make_WsContext(
yield,
request,
backend_,
subscriptions_.lock(),
balancer_,
etl_,
shared_from_this(),
*range,
counters_,
*ip);
if (!context)
return sendError(RPC::Error::rpcBAD_SYNTAX);
response = getDefaultWsResponse(id);
auto start = std::chrono::system_clock::now();
auto v = RPC::buildResponse(*context);
auto end = std::chrono::system_clock::now();
auto us = std::chrono::duration_cast<std::chrono::microseconds>(
end - start);
logDuration(*context, us);
if (auto status = std::get_if<RPC::Status>(&v))
{
counters_.rpcErrored(context->method);
auto error = RPC::make_error(*status);
if (!id.is_null())
error["id"] = id;
error["request"] = request;
response = error;
}
else
{
counters_.rpcComplete(context->method, us);
response["result"] = std::get<boost::json::object>(v);
}
}
catch (Backend::DatabaseTimeout const& t)
{
BOOST_LOG_TRIVIAL(error) << __func__ << " Database timeout";
auto range = backend_->fetchLedgerRange();
if (!range)
return sendError(RPC::Error::rpcNOT_READY);
std::optional<RPC::Context> context = RPC::make_WsContext(
yield,
request,
backend_,
subscriptions_.lock(),
balancer_,
etl_,
shared_from_this(),
*range,
counters_,
*ip);
if (!context)
return sendError(RPC::Error::rpcBAD_SYNTAX);
response = getDefaultWsResponse(id);
auto start = std::chrono::system_clock::now();
auto v = RPC::buildResponse(*context);
auto end = std::chrono::system_clock::now();
auto us = std::chrono::duration_cast<std::chrono::microseconds>(
end - start);
logDuration(*context, us);
if (auto status = std::get_if<RPC::Status>(&v))
{
counters_.rpcErrored(context->method);
auto error = RPC::make_error(*status);
if (!id.is_null())
error["id"] = id;
error["request"] = request;
response = error;
}
else
{
counters_.rpcComplete(context->method, us);
response["result"] = std::get<boost::json::object>(v);
}
}
catch (std::exception const& e)