Re: optimize lookups in snapshot [sub]xip arrays

From: Nathan Bossart <nathandbossart(at)gmail(dot)com>
To: Zhang Mingli <zmlpostgres(at)gmail(dot)com>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: optimize lookups in snapshot [sub]xip arrays
Date: 2022-07-25 04:08:56
Message-ID: 20220725040856.GB4085281@nathanxps13
Views: Raw Message | Whole Thread | Download mbox | Resend email
Thread:
Lists: pgsql-hackers

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

In response to

Responses

Browse pgsql-hackers by date

  From Date Subject
Next Message jian he 2022-07-25 04:18:12 COPY FROM FORMAT CSV FORCE_NULL(*) ?
Previous Message Richard Guo 2022-07-25 03:51:40 Re: ReadRecentBuffer() is broken for local buffer