Re: WIP: Avoid creation of the free space map for small tables

From: Mithun Cy <mithun(dot)cy(at)enterprisedb(dot)com>
To: John Naylor <jcnaylor(at)gmail(dot)com>
Cc: Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: WIP: Avoid creation of the free space map for small tables
Date: 2019-01-04 02:57:54
Message-ID: CAD__OugoaaAje8VpmC5Lc3rHOGEF2j-+K=6i+36Y-qhkZgKuNw@mail.gmail.com
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On Sun, Dec 30, 2018 at 3:49 AM John Naylor <jcnaylor(at)gmail(dot)com> wrote:
> On 12/29/18, Mithun Cy <mithun(dot)cy(at)enterprisedb(dot)com> wrote:
> That's curious, because once the table exceeds the threshold, it would
> be allowed to update the FSM, and in the process write 3 pages that it
> didn't have to in the 4 page test. The master branch has the FSM
> already, so I would expect the 8 page case to regress more.

I tested with configuration HEAP_FSM_CREATION_THRESHOLD = 4 and just
tried to insert till 8 blocks to see if regression is carried on with
further inserts.

> What I can do later is provide a supplementary patch to go on top of
> mine that only checks the last block. If that improves performance,
> I'll alter my patch to only check every other page.

Running callgrind for same test shows below stats
Before patch
==========
Number of calls function_name
2000 heap_multi_insert
2000 RelationGetBufferForTuple
3500 ReadBufferBI

After Patch
=========
Number of calls function_name
2000 heap_multi_insert
2000 RelationGetBufferForTuple
5000 ReadBufferBI

I guess Increase in ReadBufferBI() calls might be the reason which is
causing regression. Sorry I have not investigated it. I will check
same with your next patch!

--
Thanks and Regards
Mithun Chicklore Yogendra
EnterpriseDB: http://www.enterprisedb.com

Attachment Content-Type Size
callgrind_report.zip application/zip 302.5 KB

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