Re: Poor plan choice in prepared statement

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.