Don Baccus wrote:
> Zeugswetter Andreas SB SD wrote:
>
>
> > This is one of the main problems of the current optimizer which imho rather
> > aggressively chooses seq scans over index scans. During high load this does
> > not pay off.
>
>
> Bingo ... dragging huge tables through the buffer cache via a sequential
> scan guarantees that a) the next query sequentially scanning the same
> table will have to read every block again (if the table's longer than
> available PG and OS cache) b) on a high-concurrency system other queries
> end up doing extra I/O, too.
>
> Oracle partially mitigates the second effect by refusing to trash its
> entire buffer cache on any given sequential scan. Or so I've been told
> by people who know Oracle well. A repeat of the sequential scan will
> still have to reread the entire table but that's true anyway if the
> table's at least one block longer than available cache.
That is on our TODO list, at least.
-- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610)
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