Re: PostgreSQL strugling during high load

Mindaugas Riauba wrote:

>>The "vacuum cost" parameters can be adjusted to make vacuums fired
>>by pg_autovacuum less of a burden.  I haven't got any specific numbers
>>to suggest, but perhaps someone else does.
>>
>>
>
>  It looks like that not only vacuum causes our problems. vacuum_cost
>seems to lower vacuum impact but we are still noticing slow queries "storm".
>We are logging queries that takes >2000ms to process.
>  And there is quiet periods and then suddenly 30+ slow queries appears in
>log within the same second. What else could cause such behaviour? WAL log
>switch? One WAL file seems to last <1 minute.
>
>

How long are these quite periods?  Do the "strom" periods correspond to
pg_autovacuum loops?  I have heard from one person who had LOTS of
databases and tables that caused the pg_autovacuum to create a noticable
load just updateing all its stats.  The solution in that case was to add
a small delay insidet the inner pg_autovacuum loop.