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Re: Avoiding bad prepared-statement plans.

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Greg Stark <gsstark(at)mit(dot)edu>
Cc: Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Robert Haas <robertmhaas(at)gmail(dot)com>, Bart Samwel <bart(at)samwel(dot)tk>, Jeroen Vermeulen <jtv(at)xs4all(dot)nl>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Avoiding bad prepared-statement plans.
Date: 2010-02-16 20:17:32
Message-ID: 201002162017.o1GKHWa08835@momjian.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Greg Stark wrote:
> On Mon, Feb 15, 2010 at 7:11 PM, Bruce Momjian <bruce(at)momjian(dot)us> wrote:
> > 1. Why do we only do bind-level planning for anonymous wire-level queries?
> >
> > 2. I realize we did anonymous-only because that was the only way we had
> > in the protocol to _signal_ bind-time planning, but didn't we think of
> > this when we were implementing the wire-level protocol?
> 
> Is there any other difference between anonymous and non-anonymous
> queries? If this is the only major difference do we need to separate
> them? Is there any particular reason a driver would need two prepared
> queries if they're both just going to be planned at execution time?

Well, anonymous prepared queries are replanned for _every_ bind, so I
don't see a huge value in allowing multiple unnamed queries, except you
have to re-send the old query to prepare if you need to reuse it.

In fact, this behavior was not totally clear so I updated the
documentation a little with the attached patch.

> Incidentally, can you have two active anonymous portals at the same time?

No, the first one is deleted when the second is created, i.e., our docs
have:

	An unnamed prepared statement lasts only until the next Parse statement
	specifying the unnamed statement as destination is issued.  (Note that a
	simple Query message also destroys the unnamed statement.) 

-- 
  Bruce Momjian  <bruce(at)momjian(dot)us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + If your life is a hard drive, Christ can be your backup. +

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