Horton

Re: ResourceOwner refactoring

Heikki Linnakangas <hlinnaka@iki.fi>

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From: Heikki Linnakangas <hlinnaka@iki.fi>
To: Michael Paquier <michael@paquier.xyz>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>, Kyotaro Horiguchi <horikyota.ntt@gmail.com>, Andres Freund <andres@anarazel.de>
Date: 2020-11-18T08:50:08Z
Lists: pgsql-hackers 
On 18/11/2020 10:06, Michael Paquier wrote:
> On Tue, Nov 17, 2020 at 04:21:29PM +0200, Heikki Linnakangas wrote:
>> Attached patch refactors the ResourceOwner internals to do that.
> 
> + * Size of the small fixed-size array to hold most-recently remembered resources.
>    */
> -#define RESARRAY_INIT_SIZE 16
> +#define RESOWNER_ARRAY_SIZE 8
> Why did you choose this size for the initial array?

Just a guess. The old init size was 16 Datums. The entries in the new 
array are twice as large, Datum+pointer.

The "RESOWNER_STATS" #ifdef blocks can be enabled to check how many 
lookups fit in the array. With pgbench, RESOWNER_ARRAY_SIZE 8:

RESOWNER STATS: lookups: array 235, hash 32

If RESOWNER_ARRAY_STATS is increased to 16, all the lookups fit in the 
array. But I haven't done any benchmarking to see which is faster.

BTW, I think there would be an easy win in the hashing codepath, by 
changing to a cheaper hash function. Currently, with or without this 
patch, we use hash_any(). Changing that to murmurhash32() or something 
similar would be a drop-in replacement.

- Heikki

Commits

  1. Make RelationFlushRelation() work without ResourceOwner during abort

  2. Fix bug in bulk extending temp relation after failure

  3. Add missing PGDLLIMPORT markings

  4. Add test_dsa module.

  5. Clear CurrentResourceOwner earlier in CommitTransaction.

  6. Fix dsa.c with different resource owners.

  7. Fix bug in the new ResourceOwner implementation.

  8. Change pgcrypto to use the new ResourceOwner mechanism.

  9. Use a faster hash function in resource owners.

  10. Make ResourceOwners more easily extensible.

  11. Move a few ResourceOwnerEnlarge() calls for safety and clarity.