On Wed, Feb 15, 2012 at 1:35 AM, Jay Levitt <jay.lev...@gmail.com> wrote:
> We need to do a few bulk updates as Rails migrations. We're a typical > read-mostly web site, so at the moment, our checkpoint settings and WAL are > all default (3 segments, 5 min, 16MB), and updating a million rows takes 10 > minutes due to all the checkpointing. > > We have no replication or hot standbys. As a consumer-web startup, with > no SLA, and not a huge database, and if we ever do have to recover from > downtime it's ok if it takes longer.. is there a reason NOT to always run > with something like checkpoint_segments = 1000, as long as I leave the > timeout at 5m? > Still checkpoints keep occurring every 5 mins. Anyways checkpoint_segments=1000 is huge, this implies you are talking about 16MB * 1000 = 16000MB worth pg_xlog data, which is not advisable from I/O perspective and data loss perspective. Even in the most unimaginable case if all of these 1000 files get filled up in less than 5 mins, there are chances that system will slow down due to high IO and CPU. You may think of increasing checkpoint_timeout as well, but, some monitoring and analysis is needed to arrive at a number. What does pg_stat_bgwriter say about checkpoints ? Do you have log_checkpoints enabled ? Thanks VB
