Re: optimize lookups in snapshot [sub]xip arrays

On Sun, Jul 24, 2022 at 12:48:25PM +0800, Zhang Mingli wrote:
> If snaphost->suboverflowed is  false then the subxcnt must be less than PGPROC_MAX_CACHED_SUBXIDS which is 64 now.
> 
> And we won’t use hash if the xcnt is less than XIP_HASH_MIN_ELEMENTS which is 128 currently during discussion.
> 
> So that, subxid’s hash table will never be used, right?

This array will store up to TOTAL_MAX_CACHED_SUBXIDS transactions, which
will typically be much greater than 64.  When there isn't any overflow,
subxip stores all of the subxids for all of the entries in the procarray.

-- 
Nathan Bossart
Amazon Web Services: https://aws.amazon.com