Re: optimize lookups in snapshot [sub]xip arrays - Mailing list pgsql-hackers

From Zhang Mingli
Subject Re: optimize lookups in snapshot [sub]xip arrays
Date
Msg-id E5777552-8152-49B7-8F82-5C6FB6287D90@gmail.com
Whole thread Raw
In response to Re: optimize lookups in snapshot [sub]xip arrays  (Nathan Bossart <nathandbossart@gmail.com>)
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Got it, thanks.



Regards,
Zhang Mingli



> On Jul 25, 2022, at 12:08, Nathan Bossart <nathandbossart@gmail.com> wrote:
>
> 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




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