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From: Jeff Davis <pgsql@j-davis.com>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: Thomas Munro <thomas.munro@gmail.com>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Cc: Melanie Plageman <melanieplageman@gmail.com>
Cc: HeikkiLinnakangas <hlinnaka@iki.fi>
Subject: Re: Trouble with hashagg spill I/O pattern and costing
Date: Tue, 26 May 2020 17:40:19 -0700
Message-ID: <0589f869969de2f3e9713689159c7c4fbe1fcfa5.camel@j-davis.com> (raw)
In-Reply-To: <20200526191511.d7pwz4awrvdm4p6j@development>
References: <20200521191318.gw3xjivrxracvzmg@development>
	<8619437df796903e64c8479e299d13ebacb5fbe0.camel@j-davis.com>
	<20200521214122.6opovye4mnbqczlc@development>
	<20200525021045.dilgcsmgiu4l5jpa@development>
	<20200525121722.6wzcelweefyuwg54@development>
	<2df2e0728d48f498b9d6954b5f9080a34535c385.camel@j-davis.com>
	<20200525225909.aifxjm53hw4xyzxd@development>
	<CA+hUKG+q3Ma+sTKn2316Ofof6u21hh0cGJHcJ-fAnLxw=LXevw@mail.gmail.com>
	<20200526141524.ohtvrp23vxosgivl@development>
	<e913544f6c236d37e8b0597cabd086570b5806f2.camel@j-davis.com>
	<20200526191511.d7pwz4awrvdm4p6j@development>

On Tue, 2020-05-26 at 21:15 +0200, Tomas Vondra wrote:
> Yeah. I agree prefetching is definitely out of v13 scope. It might be
> interesting to try how useful would it be, if you're willing to spend
> some time on a prototype.

I think a POC would be pretty quick; I'll see if I can hack something
together.

> I think it's pretty much ready to go.

Committed with max of 128 preallocated blocks. Minor revisions.

> 
> As for the tlist fix, I think that's mostly ready too - the one thing
> we
> should do is probably only doing it for AGG_HASHED. For AGG_SORTED
> it's
> not really necessary.

Melanie previously posted a patch to avoid spilling unneeded columns,
but it introduced more code:


https://www.postgresql.org/message-id/CAAKRu_aefEsv+UkQWqu+ioEnoiL2LJu9Diuh9BR8MbyXuZ0j4A@mail.gmail...

and it seems that Heikki also looked at it. Perhaps we should get an
acknowledgement from one of them that your one-line change is the right
approach?

Regards,
	Jeff Davis







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  Subject: Re: Trouble with hashagg spill I/O pattern and costing
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