From: Merlin Moncure <mmoncure@gmail.com>
To: theo@flame.co.za
Cc: pgsql-performance@postgresql.org
Cc: andrew@supernews.com
Subject: Re: Performance problems with prepared statements
Date: Thu, 11 Oct 2007 16:04:01 -0400
Message-ID: <b42b73150710111304m161814cds984a7c525ff87241@mail.gmail.com> (raw)
In-Reply-To: <slrnfgsqpi.27gg.andrew+nonews@atlantis.supernews.net>
References: <1192027540.2495.3.camel@localhost.localdomain>
<470CE918.4060608@dalibo.com>
<1192044840.2549.21.camel@fedmac>
<slrnfgsqpi.27gg.andrew+nonews@atlantis.supernews.net>
On 10/11/07, Andrew - Supernews <andrew+nonews@supernews.com> wrote:
> On 2007-10-10, Theo Kramer <theo@flame.co.za> wrote:
> > When doing a 'manual' prepare and explain analyze I get the following
> >
> > rascal=# prepare cq (char(12), smallint, integer) as SELECT oid,
> > calllog_mainteng, calllog_phase, calllog_self FROM calllog
> > WHERE calllog_mainteng = $1
> > AND calllog_phase = $2
> > AND calllog_self < $3
> > OR calllog_mainteng = $1
> > AND calllog_phase < $2
> > ORDER BY calllog_mainteng DESC,
> > calllog_phase DESC,
> > calllog_self DESC limit 25;
> > PREPARE
>
> When you do this from the application, are you passing it 3 parameters,
> or 5? The plan is clearly taking advantage of the fact that the two
> occurrences of $1 and $2 are known to be the same value; if your app is
> using some interface that uses ? placeholders rather than numbered
> parameters, then the planner will not be able to make this assumption.
>
> Also, from the application, is the LIMIT 25 passed as a constant or is that
> also a parameter?
also, this looks a bit like a drilldown query, which is ordering the
table on 2+ fields. if that's the case, row wise comparison is a
better and faster approach. is this a converted cobol app?
merlin
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To: pgsql-performance@postgresql.org
Cc: mmoncure@gmail.com, theo@flame.co.za, andrew@supernews.com
Subject: Re: Performance problems with prepared statements
In-Reply-To: <b42b73150710111304m161814cds984a7c525ff87241@mail.gmail.com>
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