hello everyone ,
i has been add to you guys' mail list by accident, i don't how to
refuse to receive your mails, would you please help me to remove my mail
address form mail group [EMAIL PROTECTED]
i appreciatewhat you will do for me. (my mail address:
[EMAIL PROTECTED])
thanks .
From: Csaba Nagy [EMAIL PROTECTED]
To: Peter Eisentraut [EMAIL PROTECTED]
CC: postgres hackers pgsql-hackers@postgresql.org
Subject: Re: [HACKERS] Prepared statements considered harmful
Date: Thu, 31 Aug 2006 14:52:05 +0200
On Thu, 2006-08-31 at 14:32, Peter Eisentraut wrote:
Am Donnerstag, 31. August 2006 14:11 schrieb Csaba Nagy:
How about prepared means really prepared... in the sense of
parsed,
analyzed all sensible plans, and save a meta-plan which based on
current
statistics and parameter values chooses one of the considered (and
cached) plans ?
I don't think this could solve one particularly frequent problem which
is that
pattern matching queries don't get along with prepared plans if the
search
pattern isn't known at planning time.
Why not ? I specifically said you would prepare a few sensible plans
based on statistics/expected variations of the statistics, and parameter
value ranges which would trigger different plans.
So for the like query case you could save 2 plans, one for the indexable
case, one for the not indexable case. Then at runtime you choose the
proper one based on the pattern value. The meta-plan I mentioned would
be a collection of plans with rules to choose the right one at run time
based on parameter values and perhaps the current statistics.
This of course would need a lot more preparation time than just prepare
one plan, but that's why you want to do it upfront and then cache the
results. A central plan repository mentioned in other posts would fit
nicely here... and you could use prepared plans for non-parameterized
queries too by simply considering the constants as parameters, to
increase the chances for a prepared plan reuse - this of course for
complex enough queries.
Cheers,
Csaba.
---(end of broadcast)---
TIP 6: explain analyze is your friend
---(end of broadcast)---
TIP 5: don't forget to increase your free space map settings
