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Re: Poor plan choice in prepared statement

From: bricklen <bricklen(at)gmail(dot)com>
To: "Scott Marlowe" <scott(dot)marlowe(at)gmail(dot)com>
Cc: "Merlin Moncure" <mmoncure(at)gmail(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Poor plan choice in prepared statement
Date: 2008-12-30 20:14:34
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
Hi Scott,

On Tue, Dec 30, 2008 at 12:09 PM, Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com> wrote:
> On Tue, Dec 30, 2008 at 12:42 PM, Merlin Moncure <mmoncure(at)gmail(dot)com> wrote:
>> On Tue, Dec 30, 2008 at 1:59 PM, bricklen <bricklen(at)gmail(dot)com> wrote:
>>> Hi, I am re-posting my question here after trying to find a solution
>>> in the PHP pgsql list with no luck.
>>> I am experiencing some performance issues that I think are stemming
>>> from prepared statements. I have a pretty simple query:
>>> -- bad plan, from prepared statement
>>> --
>>> dev=# prepare fooplan (date,date,int,int) as
>>> dev-# SELECT cl.idOffer AS campaign, cl.idAffiliate AS affiliate,
>>> cl.idCreative AS creative, cl.subid, cl.datetime
>>> dev-# FROM click AS cl LEFT JOIN conversion AS co ON cl.clickGenerated
>>> = co.clickGenerated
>>> dev-# WHERE cl."date" >= $1
>>> dev-# AND cl."date" <= $2
>>> dev-# AND cl.idAffiliate = $3
>>> dev-# LIMIT $4;
>> Your problem is that the query as written is hard to plan.  The
>> database has no idea what you pass in, it has to guess.  (IMO, It
>> almost always guesses wrong...I think it should assume 1 row
>> returned).  Also, the db has no idea what you want to pass in at plan
>> time for date.
> One of the things you can try here is to build your query then execute
> it so it has to be planned each time.

Yeah, I've tested that in the application itself and it worked
correctly. I am trying to discover a way to use bind variables in PHP
without using the prepare function (to block sql injection), or if I
must use the prepare function, then force it to replan each time
somehow. That's part of where I'm stuck (and I'm no php guy).

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