Horton

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

Pavel Stehule <pavel.stehule@gmail.com>

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From: Pavel Stehule <pavel.stehule@gmail.com>
To: Noah Misch <noah@leadboat.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: 2011-02-08T07:00:42Z
Lists: pgsql-hackers 
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.

Regards

Pavel Stehule

>
> Tom also expressed concern over performance:
> http://archives.postgresql.org/message-id/24266.1295462892@sss.pgh.pa.us
>
> Not sure what's next.
>
> nm
>