On Tue, Sep 10, 2013 at 11:04:21AM -0400, David Whittaker wrote: > Hi All, > > I've been seeing a strange issue with our Postgres install for about a year > now, and I was hoping someone might be able to help point me at the cause. > At what seem like fairly random intervals Postgres will become unresponsive > to the 3 application nodes it services. These periods tend to last for 10 - > 15 minutes before everything rights itself and the system goes back to > normal. > > During these periods the server will report a spike in the outbound > bandwidth (from about 1mbs to about 5mbs most recently), a huge spike in > context switches / interrupts (normal peaks are around 2k/8k respectively, > and during these periods they‘ve gone to 15k/22k), and a load average of > 100+. CPU usage stays relatively low, but it’s all system time reported, > user time goes to zero. It doesn‘t seem to be disk related since we’re > running with a shared_buffers setting of 24G, which will fit just about our > entire database into memory, and the IO transactions reported by the > server, as well as the disk reads reported by Postgres stay consistently > low. > > We‘ve recently started tracking how long statements take to execute, and > we’re seeing some really odd numbers. A simple delete by primary key, for > example, from a table that contains about 280,000 rows, reportedly took > 18h59m46.900s. An update by primary key in that same table was reported as > 7d 17h 58m 30.415s. That table is frequently accessed, but obviously those > numbers don't seem reasonable at all. > > Some other changes we've made to postgresql.conf: > > synchronous_commit = off > > maintenance_work_mem = 1GB > wal_level = hot_standby > wal_buffers = 16MB > > max_wal_senders = 10 > > wal_keep_segments = 5000 > > checkpoint_segments = 128 > > checkpoint_timeout = 30min > > checkpoint_completion_target = 0.9 > > max_connections = 500 > > The server is a Dell Poweredge R900 with 4 Xeon E7430 processors, 48GB of > RAM, running Cent OS 6.3. > > So far we‘ve tried disabling Transparent Huge Pages after I found a number > of resources online that indicated similar interrupt/context switch issues, > but it hasn’t resolve the problem. I managed to catch it happening once and > run a perf which showed: > > > + 41.40% 48154 postmaster 0x347ba9 f 0x347ba9 > + 9.55% 10956 postmaster 0x2dc820 f > set_config_option > + 8.64% 9946 postmaster 0x5a3d4 f writeListPage > + 5.75% 6609 postmaster 0x5a2b0 f > ginHeapTupleFastCollect > + 2.68% 3084 postmaster 0x192483 f > build_implied_join_equality > + 2.61% 2990 postmaster 0x187a55 f > build_paths_for_OR > + 1.86% 2131 postmaster 0x794aa f > get_collation_oid > + 1.56% 1822 postmaster 0x5a67e f > ginHeapTupleFastInsert > + 1.53% 1766 postmaster 0x1929bc f > distribute_qual_to_rels > + 1.33% 1558 postmaster 0x249671 f cmp_numerics > > I‘m not sure what 0x347ba9 represents, or why it’s an address rather than a > method name. > > That's about the sum of it. Any help would be greatly appreciated and if > you want any more information about our setup, please feel free to ask. > > Thanks, > Dave Hi Dave, A load average of 100+ means that you have that many processes waiting to run yet you only have 16 cpus. You really need to consider using a connection pooler like pgbouncer to keep your connection count in the 16-32 range. Regards, Ken -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
