Horton

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

Mithun Cy <mithun.cy@enterprisedb.com>

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From: Mithun Cy <mithun.cy@enterprisedb.com>
To: John Naylor <jcnaylor@gmail.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2019-01-04T02:57:54Z
Lists: pgsql-hackers

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On Sun, Dec 30, 2018 at 3:49 AM John Naylor <jcnaylor@gmail.com> wrote:
> On 12/29/18, Mithun Cy <mithun.cy@enterprisedb.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

Commits

  1. Improve code comments in b0eaa4c51b.

  2. During pg_upgrade, conditionally skip transfer of FSMs.

  3. Add more tests for FSM.

  4. Doc: Update the documentation for FSM behavior for small tables.

  5. Make FSM test portable.

  6. Avoid creation of the free space map for small heap relations, take 2.

  7. Move page initialization from RelationAddExtraBlocks() to use, take 2.

  8. Avoid creation of the free space map for small heap relations.

  9. In bootstrap mode, don't allow the creation of files if they don't already