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: Amit Kapila <amit.kapila16@gmail.com>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2018-12-03T05:45:01Z
Lists: pgsql-hackers 
On 12/3/18, Amit Kapila <amit.kapila16@gmail.com> wrote:
> On Mon, Dec 3, 2018 at 9:46 AM Amit Kapila <amit.kapila16@gmail.com> wrote:
>>
>> On Thu, Nov 29, 2018 at 3:07 PM John Naylor <jcnaylor@gmail.com> wrote:
>> >
>>
> v8 code:
> +fsm_local_set(Relation rel, BlockNumber new_nblocks)
> +{
> + BlockNumber blkno,
> + cached_target_block;
> +
> + /*
> + * Mark blocks available starting after the last block number we have
> + * cached, and ending at the current last block in the relation.
> + * When we first set the map, this will flag all blocks as available
> + * to try.  If we reset the map while waiting for a relation
> + * extension lock, this will only flag new blocks as available,
> + * if any were created by another backend.
> + */
> + for (blkno = fsm_local_map.nblocks; blkno < new_nblocks; blkno++)
> + fsm_local_map.map[blkno] = FSM_LOCAL_AVAIL;
>
> v9 code:
> +static void
> +fsm_local_set(Relation rel, BlockNumber nblocks)
> +{
> + BlockNumber blkno,
> + cached_target_block;
> +
> + for (blkno = 0; blkno < nblocks; blkno++)
> + fsm_local_map.map[blkno] = FSM_LOCAL_AVAIL;
>
> What is the reason for the above code change in the latest patch version?

Per your recent comment, we no longer check relation size if we waited
on a relation extension lock, so this is essentially a reversion to an
earlier version. Keeping v8 would have the advantage that it'd be
simple to change our minds about this. Do you have an opinion about
that?

> It would be good if you add few comments atop functions
> GetPageWithFreeSpace, RecordAndGetPageWithFreeSpace and
> RecordPageWithFreeSpace about their interaction with local map.

Good idea, will do.

-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