hcq/MaxScale
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

MXS-3892: Limit concurrent mapping of databases

Browse Source 
As there are no practical benefits to multiple sessions for the same user
mapping the databases at the same time, limiting them to one update per
user is sensible. This is especially true now that we know the
information_schema tables aren't the most efficient things in the world.

The current code implements this rate limiting by closing any extra
sessions that would start a second update. The final implementation should
suspend them for the duration of the update as it is far more
user-friendly.

The limits are currently global as the shard caches are also global. This
is a performance bottleneck and it could be solved by storing the shard
cache inside of a mxs::WorkerGlobal instead of having it as a global
cache.
This commit is contained in:
Markus Mäkelä
2021-12-23 08:44:29 +02:00
parent d57de28199
commit 41c2a6ee8e
4 changed files with 92 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files

32
server/modules/routing/schemarouter/schemaroutersession.cc
View File

@ -45,7 +45,8 @@ SchemaRouterSession::SchemaRouterSession(MXS_SESSION* session,
, m_backends(backends)
, m_config(router->m_config)
, m_router(router)
, m_shard(m_router->m_shard_manager.get_shard(get_cache_key(), m_config->refresh_min_interval))
, m_key(get_cache_key())
, m_shard(m_router->m_shard_manager.get_shard(m_key, m_config->refresh_min_interval))
, m_state(0)
, m_sent_sescmd(0)
, m_replied_sescmd(0)
@ -111,6 +112,11 @@ void SchemaRouterSession::close()
}
}
if (m_state & INIT_MAPPING)
{
m_router->m_shard_manager.cancel_update(m_key);
}
std::lock_guard<std::mutex> guard(m_router->m_lock);
if (m_router->m_stats.longest_sescmd < m_stats.longest_sescmd)
@ -283,8 +289,26 @@ int32_t SchemaRouterSession::routeQuery(GWBUF* pPacket)
if (m_shard.empty())
{
/* Generate database list */
query_databases();
// Check if another session has managed to update the shard cache
m_shard = m_router->m_shard_manager.get_shard(m_key, m_config->refresh_min_interval);
if (m_shard.empty())
{
// No entries in the cache, try to start an update
if (m_router->m_shard_manager.start_update(m_key))
{
// No other sessions are doing an update for this user, start one
query_databases();
}
else
{
// Too many concurrent updates
// TODO: Queue this session instead of killing it
m_pSession->kill(modutil_create_mysql_err_msg(1, 0, 1096, "HY000", "Too many updates"));
return 0;
}
}
}
int ret = 0;
@ -753,7 +777,7 @@ void SchemaRouterSession::handleError(GWBUF* pMessage,
void SchemaRouterSession::synchronize_shards()
{
m_router->m_stats.shmap_cache_miss++;
m_router->m_shard_manager.update_shard(m_shard, get_cache_key());
m_router->m_shard_manager.update_shard(m_shard, m_key);
}
/**