On Tue, 7 Aug 2007, Decibel! wrote:
Is logging really the answer for that? ISTM it'd be better to provide statistics info so that you could monitor autovacuum activity with things like cricket, SNMP, etc.
There are two sides to this. One is that it's difficult to right now to tell when your performance is being whacked because autovacuum is doing something. The original version of the checkpoint + other slowdowns logging patch I submitted included a line of extra detail there so I could watch the entry/exit to every autovaccum section if the log level was cranked up to DEBUG2, motivated by the same reasons Greg Stark mentioned.
When you get into a situation where things are inexplicably slow, it's nice to do a tail on the logs and be able to figure out "oh, it's busy vacuuming X right now, no wonder". Just logging when you're going through that is good enough to let you line up the timestamps with other system activity measurements, and while difficult you can tune based just on that. And having that information easily available in the logs lets almost any level of user watch what's going on.
Actually tuning that behavior out of the system altogether is easier done by collecting statistics, in a similar fashion to how pg_stat_bgwriter lets you track checkpoints now, but that being helpful presumes a level of monitoring sophistication that typical new installations (who need this kind of help the most) don't have. Also, given the way that the stats are often updated after the work was done, that implementation may not solve the "why am I slow right now?" side of the problem effectively.
I think both types of instrumentation are ultimately needed, but if you were only picking one I think the log entries would be the better one to start with.
-- * Greg Smith [EMAIL PROTECTED] http://www.gregsmith.com Baltimore, MD ---------------------------(end of broadcast)--------------------------- TIP 6: explain analyze is your friend