Horton

Re: pg_column_toast_chunk_id: a function to get a chunk ID of a TOASTed value

Nathan Bossart <nathandbossart@gmail.com>

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From: Nathan Bossart <nathandbossart@gmail.com>
To: Yugo NAGATA <nagata@sraoss.co.jp>
Cc: jian he <jian.universality@gmail.com>, Sergei Kornilov <sk@zsrv.org>, Nikita Malakhov <hukutoc@gmail.com>, pgsql-hackers@postgresql.org
Date: 2024-03-08T22:17:58Z
Lists: pgsql-hackers

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  1. Add pg_column_toast_chunk_id().

On Fri, Mar 08, 2024 at 03:31:55PM +0900, Yugo NAGATA wrote:
> On Thu, 7 Mar 2024 16:56:17 -0600
> Nathan Bossart <nathandbossart@gmail.com> wrote:
>> to me.  Do you think it's worth adding something like a
>> pg_column_toast_num_chunks() function that returns the number of chunks for
>> the TOASTed value, too?
> 
> If we want to know the number of chunks of a specified chunk_id,
> we can get this by the following query.
> 
> postgres=# SELECT id, (SELECT count(*) FROM pg_toast.pg_toast_16384 WHERE chunk_id = id) 
>   FROM (SELECT pg_column_toast_chunk_id(v) AS id FROM t);

Good point.  Overall, I think this patch is in decent shape, so I'll aim to
commit it sometime next week.

> +{ oid => '8393', descr => 'chunk ID of on-disk TOASTed value',
> +  proname => 'pg_column_toast_chunk_id', provolatile => 's', prorettype => 'oid',
> +  proargtypes => 'any', prosrc => 'pg_column_toast_chunk_id' },

Note to self: this change requires a catversion bump.

> +INSERT INTO test_chunk_id(v1,v2)
> +  VALUES (repeat('x', 1), repeat('x', 2048));

Is this guaranteed to be TOASTed for all possible page sizes?

-- 
Nathan Bossart
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