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

From: Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Noah Misch <noah(at)leadboat(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Re: patch: fix performance problems with repated decomprimation of varlena values in plpgsql
Date: 2011-02-08 16:05:01
Message-ID: AANLkTimBSh1=k16WmDGXKr6QjP60h2+ks52DF1ZsQRwW@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
2011/2/8 Robert Haas <robertmhaas(at)gmail(dot)com>:
> On Mon, Feb 7, 2011 at 11:52 PM, Noah Misch <noah(at)leadboat(dot)com> wrote:
>> 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
>>
>> Tom also expressed concern over performance:
>> http://archives.postgresql.org/message-id/24266.1295462892@sss.pgh.pa.us
>>
>> Not sure what's next.
>
> Well, Pavel's subsequent reply suggested that he didn't test exactly
> this thing, so maybe there's hope.
>
> Or maybe not.  If Tom thought one branch inside exec_eval_datum() was
> going to be too expensive, four isn't going to be better.
>
> But I think we're out of time to work on this for this cycle.  Even if
> my latest idea is brilliant (and it may not be), we still have to test
> it in a variety of cases and get consensus on it, which seems like
> more than we can manage right now.  I think it's time to mark this one
> Returned with Feedback, or perhaps Rejected would be more accurate in
> this instance.

if you have a briliant idea, then, please, send a path :). There was
more ideas, and I am little bit lost.

I'll have a  time on weekend, and I can do some tests.

Regards

Pavel Stehule



>
> --
> Robert Haas
> EnterpriseDB: http://www.enterprisedb.com
> The Enterprise PostgreSQL Company
>

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