From: Zhang Mingli <zmlpostgres@gmail.com>
To: Nathan Bossart <nathandbossart@gmail.com>
Cc: pgsql-hackers@postgresql.org
Subject: Re: optimize lookups in snapshot [sub]xip arrays
Date: Mon, 25 Jul 2022 12:28:23 +0800
Message-ID: <E5777552-8152-49B7-8F82-5C6FB6287D90@gmail.com> (raw)
In-Reply-To: <20220725040856.GB4085281@nathanxps13>
References: <20220713170950.GA3116318@nathanxps13>
<76ACEAF0-8050-41D5-B2F5-01164533BE99@gmail.com>
<20220725040856.GB4085281@nathanxps13>
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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To: pgsql-hackers@postgresql.org
Cc: zmlpostgres@gmail.com, nathandbossart@gmail.com
Subject: Re: optimize lookups in snapshot [sub]xip arrays
In-Reply-To: <E5777552-8152-49B7-8F82-5C6FB6287D90@gmail.com>
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