On Wed, 14 Aug 2002 19:53:19 +0200, Christian Mock <cm@coretec.at>
wrote:
>Where's the big number of "Deleted" tuples coming from?
From repeatedly
> UPDATE event_stats SET count = count + x_count
> WHERE stat_id = result.stat_id;
Due to MVCC Postgres treats an UPDATE much like a DELETE and an
INSERT. I suspect the deleted tuples get in the way, when the UNIQUE
constraint is checked. This explains the linear increase of time per
tuple. I guess you are inserting sorted by (c1, c2, c3) - or at least
in large chunks of equal (c1, c2, c3) - and the "drops" in your
diagram occur whenever (c1, c2, c3) - or whatever the unique columns
on event_stats are - changes.
For now you have already found a solution/workaround. In 7.3 this can
be expected to work better.
Servus
Manfred
