| From: | Heikki Linnakangas <hlinnaka(at)iki(dot)fi> |
|---|---|
| To: | Michael Paquier <michael(at)paquier(dot)xyz> |
| Cc: | pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de> |
| Subject: | Re: ResourceOwner refactoring |
| Date: | 2020-11-18 08:50:08 |
| Message-ID: | aabd6a93-c110-4ba2-fa2d-d6f7c44e49dd@iki.fi |
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| 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
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