Horton

Re: Re: patch: fix performance problems with repated decomprimation of varlena values in plpgsql

Noah Misch <noah@leadboat.com>

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From: Noah Misch <noah@leadboat.com>
To: Pavel Stehule <pavel.stehule@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>, Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>, Kevin Grittner <Kevin.Grittner@wicourts.gov>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2011-02-08T15:28:52Z
Lists: pgsql-hackers 
On Tue, Feb 08, 2011 at 08:00:42AM +0100, Pavel Stehule wrote:
> 2011/2/8 Noah Misch <noah@leadboat.com>:
> > On Mon, Feb 07, 2011 at 11:16:18PM -0500, Robert Haas wrote:
> >> So
> >> can we just get rid of should_be_detoasted, and have exec_eval_datum()
> >> or its callers instead test:
> >>
> >> !var->isnull && var->datatype->typbyval && var->datatype->typlen == -1
> >> && VARATT_IS_EXTENDED(var->value)
> >
> > FWIW, this is what I meant by option 2 in my summary.
> >
> >> I haven't tested this, but it's not clear that'd be measurably slower
> >> than checking a single Boolean.
> >
> > Pavel benchmarked this or something close, measuring a performance loss:
> > http://archives.postgresql.org/message-id/AANLkTikDHekc9r38w2ttzoMDr8vDaVAnr3LhqfJkEuL9@mail.gmail.com
> 
> I tested this in situation when Datum is detoasted on usage, not in
> assignment. So impact will be less.

Robert spoke of doing it on usage (exec_eval_datum()) too, though.