Thu May 27 12:36:40 PDT 2010
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Just ran into an interesting problem where I had a slave that was lagging for no apparent reason. After some digging I fired up pgspy and watched the timing of queries and noticed forwardConfirm was consistently taking a long time (1-2 seconds). The queries it issued seemed to be zippy, leaving just the notify. Sure enough: XXXX=# select * from pgstattuple('pg_listener'); -[ RECORD 1 ]------+---------- table_len | 312877056 tuple_count | 3 tuple_len | 288 tuple_percent | 0 dead_tuple_count | 44 dead_tuple_len | 4224 dead_tuple_percent | 0 free_space | 299606604 free_percent | 95.76 we've got a bit of the ol' bloat there. but wait, I'm running 8.4.2 shouldn't AV be taking care of that? Looking at pg_stat_all_tables I see last_vacuum | last_autovacuum | 2010-05-19 13:21:37.349991-04 last_analyze | 2010-05-27 14:16:39.887117-04 last_autoanalyze | 2010-05-19 13:21:37.349991-04 well shoot, that was last week! someone on irc suggested autovac cancellation so I looked at my logs and sure enough, pg_listener and autovac were NOT getting along (along with some other tables as well). after building a list of the most commonly aborted autovacs I checked those out and all had recent autovac records in pg_stat_all_tables. a vacuum full of pg_listener and we're back in business, lag immediately dropped to 0. not sure what I can do to cope with the continued cancellations - I would have thought it would have tried again shortly but apparently I was wrong. time to whip up yet another nagios alarm :( Mostly just putting this out there for others who may have run into this. btw, this is on a patched slony 1.2.17 & pg 8.4.2 -- Jeff Trout <jeff at jefftrout.com> http://www.stuarthamm.net/ http://www.dellsmartexitin.com/
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