Dear All, Thanks for all your help so far. This page was particularly helpful: http://www.westnet.com/~gsmith/content/postgresql/chkp-bgw-83.htm (does the advice for 8.3 apply unchanged to 8.4?) I'm still hitting issues with this though: sync is taking 7-10 seconds and I need to get it down to nearer 3. We're running a lightly-loaded system which has a realtime response requirement of 0.5 seconds all the time (with a few seconds permissible occasionally, but never exceeding 10). So far, I've set checkpoint_segments to 128, timeout to 10min, and completion_target to 0.8. This helps, but not as much as I'd hoped. But I haven't touched any of the other WAL or BG Writer settings. Where should I look next? Should I be looking at the BG Writer settings, or should I look at the Linux VM configuration? (eg changing /proc/sys/vm/dirty_background_ratio from 5 to 1) Or would it be most useful to try to move the WAL to a different disk? Latest messages: # tail -f /var/log/postgresql/postgresql-8.4-main.log | grep check 2009-12-08 09:12:00 GMT LOG: checkpoint starting: time 2009-12-08 09:20:09 GMT LOG: checkpoint complete: wrote 51151 buffers (8.9%); 0 transaction log file(s) added, 0 removed, 23 recycled; write=479.669 s, sync=9.852 s, total=489.553 s 2009-12-08 09:22:00 GMT LOG: checkpoint starting: time 2009-12-08 09:30:07 GMT LOG: checkpoint complete: wrote 45772 buffers (7.9%); 0 transaction log file(s) added, 0 removed, 24 recycled; write=479.706 s, sync=7.337 s, total=487.120 s 2009-12-08 09:32:00 GMT LOG: checkpoint starting: time 2009-12-08 09:40:09 GMT LOG: checkpoint complete: wrote 47043 buffers (8.2%); 0 transaction log file(s) added, 0 removed, 22 recycled; write=479.744 s, sync=9.300 s, total=489.122 s 2009-12-08 09:42:00 GMT LOG: checkpoint starting: time 2009-12-08 09:50:07 GMT LOG: checkpoint complete: wrote 48210 buffers (8.4%); 0 transaction log file(s) added, 0 removed, 23 recycled; write=479.689 s, sync=7.707 s, total=487.416 s Thanks a lot, Richard -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
