Hello dear list members, I have strange problem with my new 8.4 deployment, which I never encountered on previous 8.3 deployment. IOwait values are extremely high exactly when Postgres finishes a checkpoint. During the checkpoint itself (which is quite lengthy) IOwait is very low. Why does this happen and how to fix it? Take a look at this chart: http://kpox.s3.amazonaws.com/cpu-day.png The lates (rightest) IOwait peak corresponds to this log entry: 2010-01-08 18:40:36 CET LOG: checkpoint complete: wrote 46357 buffers (35.4%); 0 transaction log file(s) added, 0 removed, 40 recycled; write=2502.800 s, sync=79.972 s, total=2583.184 s IOwait peak starts about 18:39:30 and finishes at 18:40:30. I think all the IOwait comes during sync time, which is 80 s, according to the log entry. Config details that might be related to the problem: bgwriter_lru_maxpages = 0 # BG writer is off checkpoint_segments = 45 checkpoint_timeout = 60min checkpoint_completion_target = 0.9 I had mostly the same config with my 8.3 deployment. But hardware is different: Disk is software RAID-5 with 3 hard drives. Operating system is Ubuntu 9.10 Server x64. Thanks. Anton. -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
