From: Nathan Bossart <nathandbossart@gmail.com>
To: Zhang Mingli <zmlpostgres@gmail.com>
Cc: pgsql-hackers@postgresql.org
Subject: Re: optimize lookups in snapshot [sub]xip arrays
Date: Sun, 24 Jul 2022 21:08:56 -0700
Message-ID: <20220725040856.GB4085281@nathanxps13> (raw)
In-Reply-To: <76ACEAF0-8050-41D5-B2F5-01164533BE99@gmail.com>
References: <20220713170950.GA3116318@nathanxps13>
<76ACEAF0-8050-41D5-B2F5-01164533BE99@gmail.com>
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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To: pgsql-hackers@postgresql.org
Cc: nathandbossart@gmail.com, zmlpostgres@gmail.com
Subject: Re: optimize lookups in snapshot [sub]xip arrays
In-Reply-To: <20220725040856.GB4085281@nathanxps13>
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