Re: ResourceOwner refactoring

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