Horton

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

John Naylor <jcnaylor@gmail.com>

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From: John Naylor <jcnaylor@gmail.com>
To: Thomas Munro <thomas.munro@enterprisedb.com>
Cc: Pg Hackers <pgsql-hackers@postgresql.org>
Date: 2018-10-07T15:17:24Z
Lists: pgsql-hackers

Attachments

On 10/6/18, Thomas Munro <thomas.munro@enterprisedb.com> wrote:
> On Sat, Oct 6, 2018 at 7:47 AM John Naylor <jcnaylor@gmail.com> wrote:
>> A while back, Robert Haas noticed that the space taken up by very
>> small tables is dominated by the FSM [1]. Tom suggested that we could
>> prevent creation of the FSM until the heap has reached a certain
>> threshold size [2]. Attached is a WIP patch to implement that. I've
>> also attached a SQL script to demonstrate the change in behavior for
>> various scenarios.
>
> Hi John,
>
> You'll need to tweak the test in contrib/pageinspect/sql/page.sql,
> because it's currently asserting that there is an FSM on a small table
> so make check-world fails.

Whoops, sorry about that; the attached patch passes make check-world.
While looking into that, I also found a regression: If the cached
target block is the last block in the relation and there is no free
space, that block will be tried twice. That's been fixed as well.

Thanks,
-John Naylor

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