Re: again on index usage

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.

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