pg.ddx.io pgsql-hackers@postgresql.org mailing list archive help / color / mirror / Atom feed From: Jeff Davis <pgsql@j-davis.com>
To: jian he <jian.universality@gmail.com>
To: Corey Huinker <corey.huinker@gmail.com>
Cc: Matthias van de Meent <boekewurm+postgres@gmail.com>
Cc: Bruce Momjian <bruce@momjian.us>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Nathan Bossart <nathandbossart@gmail.com>
Cc: Magnus Hagander <magnus@hagander.net>
Cc: Stephen Frost <sfrost@snowman.net>
Cc: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
Cc: Peter Smith <smithpb2250@gmail.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Cc: Tomas Vondra <tomas.vondra@enterprisedb.com>
Cc: alvherre@alvh.no-ip.org
Subject: Re: Statistics Import and Export
Date: Fri, 11 Oct 2024 16:10:34 -0700
Message-ID: <e0660898b696b0bb77030f8b850d662ad3c663d2.camel@j-davis.com> (raw )
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On Mon, 2024-09-23 at 08:57 +0800, jian he wrote:
> newtup = heap_modify_tuple_by_cols(ctup, tupdesc, ncols,
> replaces, nulls);
>
> you just directly declared "bool nulls[3] = {false, false,
> false};"
Those must be false (not NULL), because in pg_class those are non-NULL
attributes. They must be set to something whenever we update.
> if any of (RELPAGES_ARG, RELTUPLES_ARG, RELALLVISIBLE_ARG)
> is null, should you set that null[position] to true?
If the corresponding SQL argument is NULL, we leave the existing value
unchanged, we don't set it to NULL.
> otherwise, i am confused with the variable nulls.
>
> Looking at other usage of heap_modify_tuple_by_cols, "ncols" cannot
> be
> dynamic, it should be a fixed value?
> The current implementation works, because the (bool[3] nulls) is
> always false, never changed.
> if nulls becomes {false, false, true} then "ncols" must be 3, cannot
> be 2.
heap_modify_tuple_by_cols() uses ncols to specify the length of the
values/isnull arrays. The "replaces" is an array of attribute numbers
to replace (in contrast to plain heap_modify_tuple(), which uses an
array of booleans).
We are going to replace a maximum of 3 attributes, so the arrays have a
maximum size of 3. Predeclaring the arrays to be 3 elements is just
fine even if we only use the first 1-2 elements -- it avoids a needless
heap allocation/free.
Regards,
Jeff Davis
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Cc: pgsql@j-davis.com, jian.universality@gmail.com, corey.huinker@gmail.com, boekewurm+postgres@gmail.com, bruce@momjian.us, tgl@sss.pgh.pa.us, nathandbossart@gmail.com, magnus@hagander.net, sfrost@snowman.net, ashutosh.bapat.oss@gmail.com, smithpb2250@gmail.com, pgsql-hackers@lists.postgresql.org, tomas.vondra@enterprisedb.com, alvherre@alvh.no-ip.org
Subject: Re: Statistics Import and Export
In-Reply-To: <e0660898b696b0bb77030f8b850d662ad3c663d2.camel@j-davis.com>
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