Horton

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

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, John Naylor <jcnaylor@gmail.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2018-11-02T14:07:10Z
Lists: pgsql-hackers 
Robert Haas <robertmhaas@gmail.com> writes:
> 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.

Hmm, you're assuming something not in evidence: why would that be the
algorithm?  On a FSM-less table, I'd be inclined to just check the
last page and then grow the table if the tuple doesn't fit there.
This would, in many cases, soon result in a FSM being created, but
I think that's just fine.  The point of the change is to optimize
for cases where a table *never* gets more than a few inserts.  Not, IMO,
for cases where a table gets a lot of churn but never has a whole lot of
live tuples.  In the latter scenario we are far better off having a FSM.

			regards, tom lane

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