Horton

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

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: John Naylor <jcnaylor@gmail.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2018-11-02T13:59:33Z
Lists: pgsql-hackers 
On Fri, Nov 2, 2018 at 7:23 AM Amit Kapila <amit.kapila16@gmail.com> wrote:
> > That doesn't seem like an unreasonable argument.  I'm not sure whether
> > the right threshold is 4 or something a little bigger, but I bet it's
> > not very large.  It seems important to me that before anybody thinks
> > about committing this, we construct some kind of destruction case
> > where repeated scans of the whole table are triggered as frequently as
> > possible, and then run that test with varying thresholds.
>
> Why do you think repeated scans will be a destruction case when there
> is no FSM for a small table?

That's not what I'm saying.  If we don't have the FSM, we have to
check every page of the table.  If there's a workload where that
happens a lot on a table that is just under the size threshold for
creating the FSM, then it's likely to be a worst case for this patch.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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