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 02:53:00
Message-ID: CAD__Ouj8ETKajtQC7uowSY--EUenygTPNfJU7Njbhdy9=DQf2Q@mail.gmail.com
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Thanks,

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:
> > Results are execution time(unit ms) taken by copy statement when number of
> > records equal to exact number which fit HEAP_FSM_CREATION_THRESHOLD = 4
> > pages. For fill factor 20 it is till tid (3, 43) and for scale factor 70
> > till tid (3, 157). Result is taken as a median of 10 runs.
>
> > So 2-3% consistent regression, And on every run I can see for patch v11
> > execution time is slightly more than base.
>
> Thanks for testing!
>
> > I also tried to insert more
> > records till 8 pages and same regression is observed! So I guess even
> > HEAP_FSM_CREATION_THRESHOLD = 4 is not perfect!
>
> 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.out.115655_before_patch application/octet-stream 522.5 KB
callgrind.out.115483_after_patch application/octet-stream 522.0 KB

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