Re: Interpreting vacuum verbosity

On Friday May 7 2004 12:48, Tom Lane wrote:
> "Ed L." <pgsql(at)bluepolka(dot)net> writes:
> > 2) Would this low setting of 10000 explain the behavior we saw of
> > seqscans of a perfectly analyzed table with 1000 rows requiring
> > ridiculous amounts of time even after we cutoff the I/O load?
>
> Possibly. The undersized setting would cause leakage of disk space
> (that is, new rows get appended to the end of the table even when space
> is available within the table, because the system has "forgotten" about
> that space due to lack of FSM slots to remember it in). If the physical
> size of the table file gets large enough, seqscans will take a long time
> no matter how few live rows there are. I don't recall now whether your
> VACUUM VERBOSE results showed that the physical table size (number of
> pages) was out of proportion to the actual number of live rows. But it
> sure sounds like that might have been the problem.

If it were indeed the case that we'd leaked a lot of diskspace, then after
bumping max_fsm_pages up to a much higher number (4M), will these pages
gradually be "remembered" as they are accessed by autovac and or queried,
etc? Or is a dump/reload or 'vacuum full' the only way? Trying to avoid
downtime...