From: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Jules Bean <jules(at)jellybean(dot)co(dot)uk>, Alfred Perlstein <bright(at)wintelcom(dot)net>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Performance on inserts |
Date: | 2000-10-16 04:59:47 |
Message-ID: | 200010160459.AAA01950@candle.pha.pa.us |
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Lists: | pgsql-hackers |
> Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> >> So an inner indexscan for tab1 is definitely a possible plan.
>
> > Yes, that was my point, that a nested loop could easily be involved if
> > the joined table has a restriction. Is there a TODO item here?
>
> More like a "to investigate" --- I'm not sold on the idea that a
> dynamic switch in plan types would be a win. Maybe it would be,
> but...
>
> One thing to think about is that it'd be critically dependent on having
> accurate statistics. Currently, the planner only places bets on the
> average behavior over a whole join. If you make a separate bet on each
> scan, then you open up the risk of betting wrong every time, should
> your stats be out-of-date or otherwise misleading.
I agree. Not sure how to approach this, but I am sure it is dealt with
by most database systems. Can someone find out how other db's handle
this? Is there any research on it?
--
Bruce Momjian | http://candle.pha.pa.us
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
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