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ed70ed6f71
This will allow to avoid superfluous sleep during query execution, since
this not only not desired behavoiur, but also may hang the server, since
if you will execute enough queries that will use MySQL database but will
not allow enough connections (or your MySQL server is too slow) then you
may run out of threads in the global thread pool.
Also note that right now it is possible to get deadlock when the mysql
pool is full, consider the following scenario:
- you have m1 and m2 mysql tables
- you have q1 and q2 queries, bot queries join m1 and m2
- q1 allocated connection for m1 but cannot allocate connection for m2
- q2 allocated connection for m2 but cannot allocate connection for m1
- but to resolve the lock one should give up on the locking while it is not possible right now...
And then you got no free threads and this:
# grep -h ^202 /proc/$(pgrep clickhouse-serv)/task/*/syscall | cut -d' ' -f2 | sort | uniq -c | sort -nr | head
1554 0x7ffb60b92fe8 # mutex in mysqlxx::PoolWithFailover::get
1375 0x7ffb9f1c4748 # mutex in ::PoolEntryHelper::~PoolEntryHelper from DB::MultiplexedConnections::invalidateReplica
1160 0x7ffb612918b8 # mutex in mysqlxx::PoolWithFailover::get
42 0x7ffb9f057984 # mutex in ThreadPoolImpl<std::__1::thread>::worker
*NOTE: 202 is a `futex` with WAIT*
(Went with `syscall` because debugging 10k+ threads is not easy, and
eventually it may TRAP)
366 lines
11 KiB
C++
366 lines
11 KiB
C++
#if __has_include(<mysql.h>)
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#include <mysql.h>
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#include <mysqld_error.h>
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#else
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#include <mysql/mysql.h>
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#include <mysql/mysqld_error.h>
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#endif
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#include <mysqlxx/Pool.h>
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#include <common/sleep.h>
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#include <Poco/Util/LayeredConfiguration.h>
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#include <ctime>
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namespace
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{
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inline uint64_t clock_gettime_ns(clockid_t clock_type = CLOCK_MONOTONIC)
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{
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struct timespec ts;
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clock_gettime(clock_type, &ts);
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return uint64_t(ts.tv_sec * 1000000000LL + ts.tv_nsec);
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}
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}
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namespace mysqlxx
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{
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void Pool::Entry::incrementRefCount()
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{
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if (!data)
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return;
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/// First reference, initialize thread
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if (data->ref_count.fetch_add(1) == 0)
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mysql_thread_init();
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}
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void Pool::Entry::decrementRefCount()
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{
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if (!data)
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return;
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/// We were the last user of this thread, deinitialize it
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if (data->ref_count.fetch_sub(1) == 1)
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mysql_thread_end();
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}
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Pool::Pool(const Poco::Util::AbstractConfiguration & cfg, const std::string & config_name,
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unsigned default_connections_, unsigned max_connections_,
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const char * parent_config_name_)
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: logger(Poco::Logger::get("mysqlxx::Pool"))
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, default_connections(default_connections_)
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, max_connections(max_connections_)
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{
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server = cfg.getString(config_name + ".host");
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if (parent_config_name_)
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{
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const std::string parent_config_name(parent_config_name_);
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db = cfg.getString(config_name + ".db", cfg.getString(parent_config_name + ".db", ""));
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user = cfg.has(config_name + ".user")
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? cfg.getString(config_name + ".user")
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: cfg.getString(parent_config_name + ".user");
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password = cfg.has(config_name + ".password")
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? cfg.getString(config_name + ".password")
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: cfg.getString(parent_config_name + ".password");
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if (!cfg.has(config_name + ".port") && !cfg.has(config_name + ".socket")
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&& !cfg.has(parent_config_name + ".port") && !cfg.has(parent_config_name + ".socket"))
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throw Poco::Exception("mysqlxx::Pool configuration: expected port or socket");
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port = cfg.has(config_name + ".port")
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? cfg.getInt(config_name + ".port")
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: cfg.getInt(parent_config_name + ".port", 0);
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socket = cfg.has(config_name + ".socket")
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? cfg.getString(config_name + ".socket")
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: cfg.getString(parent_config_name + ".socket", "");
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ssl_ca = cfg.has(config_name + ".ssl_ca")
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? cfg.getString(config_name + ".ssl_ca")
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: cfg.getString(parent_config_name + ".ssl_ca", "");
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ssl_cert = cfg.has(config_name + ".ssl_cert")
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? cfg.getString(config_name + ".ssl_cert")
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: cfg.getString(parent_config_name + ".ssl_cert", "");
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ssl_key = cfg.has(config_name + ".ssl_key")
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? cfg.getString(config_name + ".ssl_key")
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: cfg.getString(parent_config_name + ".ssl_key", "");
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enable_local_infile = cfg.getBool(config_name + ".enable_local_infile",
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cfg.getBool(parent_config_name + ".enable_local_infile", MYSQLXX_DEFAULT_ENABLE_LOCAL_INFILE));
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opt_reconnect = cfg.getBool(config_name + ".opt_reconnect",
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cfg.getBool(parent_config_name + ".opt_reconnect", MYSQLXX_DEFAULT_MYSQL_OPT_RECONNECT));
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}
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else
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{
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db = cfg.getString(config_name + ".db", "");
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user = cfg.getString(config_name + ".user");
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password = cfg.getString(config_name + ".password");
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if (!cfg.has(config_name + ".port") && !cfg.has(config_name + ".socket"))
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throw Poco::Exception("mysqlxx::Pool configuration: expected port or socket");
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port = cfg.getInt(config_name + ".port", 0);
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socket = cfg.getString(config_name + ".socket", "");
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ssl_ca = cfg.getString(config_name + ".ssl_ca", "");
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ssl_cert = cfg.getString(config_name + ".ssl_cert", "");
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ssl_key = cfg.getString(config_name + ".ssl_key", "");
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enable_local_infile = cfg.getBool(
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config_name + ".enable_local_infile", MYSQLXX_DEFAULT_ENABLE_LOCAL_INFILE);
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opt_reconnect = cfg.getBool(config_name + ".opt_reconnect", MYSQLXX_DEFAULT_MYSQL_OPT_RECONNECT);
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}
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connect_timeout = cfg.getInt(config_name + ".connect_timeout",
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cfg.getInt("mysql_connect_timeout",
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MYSQLXX_DEFAULT_TIMEOUT));
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rw_timeout =
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cfg.getInt(config_name + ".rw_timeout",
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cfg.getInt("mysql_rw_timeout",
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MYSQLXX_DEFAULT_RW_TIMEOUT));
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}
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Pool::~Pool()
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{
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std::lock_guard<std::mutex> lock(mutex);
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for (auto & connection : connections)
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delete static_cast<Connection *>(connection);
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}
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Pool::Entry Pool::get(uint64_t wait_timeout)
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{
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std::unique_lock<std::mutex> lock(mutex);
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uint64_t deadline = 0;
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/// UINT64_MAX -- wait indefinitely
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if (wait_timeout && wait_timeout != UINT64_MAX)
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deadline = clock_gettime_ns() + wait_timeout * 1'000'000'000;
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initialize();
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for (;;)
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{
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logger.trace("(%s): Iterating through existing MySQL connections", getDescription());
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for (auto & connection : connections)
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{
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if (connection->ref_count == 0)
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return Entry(connection, this);
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}
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logger.trace("(%s): Trying to allocate a new connection.", getDescription());
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if (connections.size() < static_cast<size_t>(max_connections))
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{
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Connection * conn = allocConnection();
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if (conn)
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return Entry(conn, this);
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logger.trace("(%s): Unable to create a new connection: Allocation failed.", getDescription());
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}
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else
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{
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logger.trace("(%s): Unable to create a new connection: Max number of connections has been reached.", getDescription());
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}
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if (!wait_timeout)
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throw Poco::Exception("mysqlxx::Pool is full (wait is disabled, see connection_wait_timeout setting)");
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if (deadline && clock_gettime_ns() >= deadline)
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throw Poco::Exception("mysqlxx::Pool is full (connection_wait_timeout is exceeded)");
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lock.unlock();
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logger.trace("(%s): Sleeping for %d seconds.", getDescription(), MYSQLXX_POOL_SLEEP_ON_CONNECT_FAIL);
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sleepForSeconds(MYSQLXX_POOL_SLEEP_ON_CONNECT_FAIL);
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lock.lock();
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}
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}
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Pool::Entry Pool::tryGet()
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{
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std::lock_guard<std::mutex> lock(mutex);
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initialize();
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/// Try to pick an idle connection from already allocated
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for (auto connection_it = connections.cbegin(); connection_it != connections.cend();)
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{
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Connection * connection_ptr = *connection_it;
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/// Fixme: There is a race condition here b/c we do not synchronize with Pool::Entry's copy-assignment operator
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if (connection_ptr->ref_count == 0)
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{
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{
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Entry res(connection_ptr, this);
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if (res.tryForceConnected()) /// Tries to reestablish connection as well
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return res;
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}
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logger.debug("(%s): Idle connection to MySQL server cannot be recovered, dropping it.", getDescription());
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/// This one is disconnected, cannot be reestablished and so needs to be disposed of.
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connection_it = connections.erase(connection_it);
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::delete connection_ptr; /// TODO: Manual memory management is awkward (matches allocConnection() method)
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}
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else
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++connection_it;
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}
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if (connections.size() >= max_connections)
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throw Poco::Exception("mysqlxx::Pool is full");
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Connection * connection_ptr = allocConnection(true);
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if (connection_ptr)
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return {connection_ptr, this};
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return {};
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}
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void Pool::removeConnection(Connection* connection)
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{
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logger.trace("(%s): Removing connection.", getDescription());
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std::lock_guard<std::mutex> lock(mutex);
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if (connection)
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{
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if (connection->ref_count > 0)
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{
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connection->conn.disconnect();
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connection->ref_count = 0;
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}
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connections.remove(connection);
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}
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}
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void Pool::Entry::disconnect()
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{
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pool->removeConnection(data);
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}
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void Pool::Entry::forceConnected() const
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{
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if (data == nullptr)
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throw Poco::RuntimeException("Tried to access NULL database connection.");
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bool first = true;
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while (!tryForceConnected())
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{
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if (first)
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first = false;
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else
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sleepForSeconds(MYSQLXX_POOL_SLEEP_ON_CONNECT_FAIL);
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pool->logger.debug("Entry: Reconnecting to MySQL server %s", pool->description);
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data->conn.connect(
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pool->db.c_str(),
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pool->server.c_str(),
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pool->user.c_str(),
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pool->password.c_str(),
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pool->port,
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pool->socket.c_str(),
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pool->ssl_ca.c_str(),
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pool->ssl_cert.c_str(),
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pool->ssl_key.c_str(),
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pool->connect_timeout,
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pool->rw_timeout,
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pool->enable_local_infile,
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pool->opt_reconnect);
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}
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}
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bool Pool::Entry::tryForceConnected() const
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{
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auto * const mysql_driver = data->conn.getDriver();
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const auto prev_connection_id = mysql_thread_id(mysql_driver);
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pool->logger.trace("Entry(connection %lu): sending PING to check if it is alive.", prev_connection_id);
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if (data->conn.ping()) /// Attempts to reestablish lost connection
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{
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const auto current_connection_id = mysql_thread_id(mysql_driver);
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if (prev_connection_id != current_connection_id)
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{
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pool->logger.debug("Entry(connection %lu): Reconnected to MySQL server. Connection id changed: %lu -> %lu",
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current_connection_id, prev_connection_id, current_connection_id);
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}
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pool->logger.trace("Entry(connection %lu): PING ok.", current_connection_id);
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return true;
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}
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pool->logger.trace("Entry(connection %lu): PING failed.", prev_connection_id);
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return false;
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}
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void Pool::initialize()
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{
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if (!initialized)
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{
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description = db + "@" + server + ":" + std::to_string(port) + " as user " + user;
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for (unsigned i = 0; i < default_connections; ++i)
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allocConnection();
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initialized = true;
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}
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}
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Pool::Connection * Pool::allocConnection(bool dont_throw_if_failed_first_time)
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{
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std::unique_ptr conn_ptr = std::make_unique<Connection>();
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try
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{
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logger.debug("Connecting to %s", description);
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conn_ptr->conn.connect(
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db.c_str(),
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server.c_str(),
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user.c_str(),
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password.c_str(),
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port,
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socket.c_str(),
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ssl_ca.c_str(),
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ssl_cert.c_str(),
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ssl_key.c_str(),
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connect_timeout,
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rw_timeout,
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enable_local_infile,
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opt_reconnect);
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}
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catch (mysqlxx::ConnectionFailed & e)
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{
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logger.error(e.what());
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if ((!was_successful && !dont_throw_if_failed_first_time)
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|| e.errnum() == ER_ACCESS_DENIED_ERROR
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|| e.errnum() == ER_DBACCESS_DENIED_ERROR
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|| e.errnum() == ER_BAD_DB_ERROR)
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{
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throw;
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}
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else
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{
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return nullptr;
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}
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}
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connections.push_back(conn_ptr.get());
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was_successful = true;
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return conn_ptr.release();
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}
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}
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