Re: force re-planning of prepared statements?

[pgdba(at)hush(dot)com]

All my data has been fully vacuumed and analyzed, so that isn't the 
problem. The problem is specifically that the incorrect plan is 
being selected, and I think that that is due to the re-use of a sub-
optimal plan.

On Mon, 29 Dec 2008 16:47:10 -0800 V S P <toreason(at)fastmail(dot)fm> 
wrote:
>Hi,
>I do not have an answer for you
>
>but, it is my understanding that
>a) PHP drops the DB connection for every HTTP request
>and then creates a new one (unless a proxy is used)
>That means that prepare statement has a perfromance benefit
>if the same SQL is used more than once per session
>
>b) if prepare by itself takes long, than may be analyzing
>tables/updating
>statistics/vaccuming at least the tables involved in the query 
>might
>help
>
>c) if b) does not help -- personally I would think that the 
>problem
>is somewhere outside the 'prepare' call (unless there is a PG bug 
>in
>that
>functionality on that version of the server)
>
>
>
>
>On Mon, 29 Dec 2008 14:17:05 -0800, pgdba(at)hush(dot)com said:
>> Hi all, I am experiencing some performance issues that I think 
>are 
>> stemming from the PDO prepared statements functions.
>> 
>> I have a pretty simple query that runs:
>> 
>> - sub-second when issued from the command line (not prepared)
>> 
>> - takes 200+ seconds when run from the command line inside a 
>> prepared statement (eg. 
>> http://www.postgresql.org/docs/8.2/interactive/sql-prepare.html)
>> 
>> - takes over 200s when run from our application, within the pdo 
>> prepared functions
>> 
>> - runs sub-second from our application if I prepend the query 
>with 
>> "explain analyze" and looking at the resulting plan, it shows 
>the 
>> same plan as when it runs quickly from the command line.
>> 
>> postgresql 8.2.11, php 5.2.1
>> 
>> What are my options here? I would like to continue to use bind 
>> variables to prevent sql injection, but I'd like to force a plan 
>re-
>> parse for every single query.
>> 
>> Any ideas?
>> 
>> 
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>  V S P
>  toreason(at)fastmail(dot)fm
>
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