Re: Very big insert/join performance problem (bacula)

Le Thursday 16 July 2009 01:56:37, Devin Ben-Hur a écrit :
> Marc Cousin wrote:
> > This mail contains the asked plans :
> > Plan 1
> > around 1 million records to insert, seq_page_cost 1, random_page_cost 4
> >
> > -> Hash (cost=425486.72..425486.72 rows=16746972 width=92)
> > (actual time=23184.196..23184.196 rows=16732049 loops=1) -> Seq Scan on
> > path (cost=0.00..425486.72 rows=16746972 width=92) (actual
> > time=0.004..7318.850 rows=16732049 loops=1)
> >
> > -> Hash (cost=1436976.15..1436976.15 rows=79104615 width=35) (actual
> > time=210831.840..210831.840 rows=79094418 loops=1) -> Seq Scan on
> > filename (cost=0.00..1436976.15 rows=79104615 width=35) (actual
> > time=46.324..148887.662 rows=79094418 loops=1)
>
> This doesn't address the cost driving plan question, but I think it's a
> bit puzzling that a seq scan of 17M 92-byte rows completes in 7 secs,
> while a seqscan of 79M 35-byte rows takes 149secs. It's about 4:1 row
> ratio, less than 2:1 byte ratio, but a 20:1 time ratio. Perhaps there's
> some terrible bloat on filename that's not present on path? If that seq
> scan time on filename were proportionate to path this plan would
> complete about two minutes faster (making it only 6 times slower instead
> of 9 :).
Much simpler than that I think : there is a bigger percentage of path that is
used all the time than of filename. The database used is the production
database, so there were other insert queries running a few minutes before I
got this plan.

But I'll give it a look today and come back with bloat and cache information
on these 2 tables.