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From: jian he <jian.universality@gmail.com>
Date: Fri, 22 Aug 2025 11:36:45 +0800
Message-ID: 
 <CACJufxEH45Rtkn=n9hjakeKEkH7ou8domh+iQHMp+18Wq_L-4g@mail.gmail.com>
Subject: Re: Add SPLIT PARTITION/MERGE PARTITIONS commands
To: Dmitry Koval <d.koval@postgrespro.ru>
Cc: Alexander Korotkov <aekorotkov@gmail.com>,
 pgsql-hackers@lists.postgresql.org
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On Thu, Aug 21, 2025 at 2:45=E2=80=AFPM jian he <jian.universality@gmail.co=
m> wrote:
>
> On Thu, Aug 21, 2025 at 10:53=E2=80=AFAM jian he <jian.universality@gmail=
.com> wrote:
> >
> > > this time, I only checked
> > > v52-0001-Implement-ALTER-TABLE-.-MERGE-PARTITIONS-.-comma.patch

hi.

+static void
+check_two_partitions_bounds_range(Relation parent,
+{
....
+
+ ereport(ERROR,
+ errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+ errmsg("lower bound of partition \"%s\" is not equal to the upper
bound of partition \"%s\"",
+   second_name->relname, first_name->relname),
+ errhint("ALTER TABLE ... MERGE PARTITIONS requires the partition
bounds to be adjacent."),
+ parser_errposition(pstate, datum->location));
+ }

I propose change it to:
        ereport(ERROR,
                errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                errmsg("can not merge partition \"%s\" together with
partition \"%s\"",
                       second_name->relname, first_name->relname),
                errdetail("lower bound of partition \"%s\" is not
equal to the upper bound of partition \"%s\"",
                          second_name->relname, first_name->relname),
                errhint("ALTER TABLE ... MERGE PARTITIONS requires the
partition bounds to be adjacent."),
                parser_errposition(pstate, datum->location));


    <para>
+     There is also an option for merging multiple table partitions into
+     a single partition using the
+     <link linkend=3D"sql-altertable-merge-partitions"><command>ALTER
TABLE ... MERGE PARTITIONS</command></link>.
+     This feature simplifies the management of partitioned tables by allow=
ing
+     users to combine partitions that are no longer needed as
+     separate entities.  It's important to note that this operation is not
+     supported for hash-partitioned tables and acquires an
+     <literal>ACCESS EXCLUSIVE</literal> lock, which could impact high-loa=
d
+     systems due to the lock's restrictive nature.  For example, we can
+     merge three monthly partitions into one quarter partition:
I am not sure last sentence "merge three monthly partitions into one
quarter partition:"
is correct.


buildExpressionExecutionStates seems not needed, same reason as
mentioned before,
code pattern aligned with ATRewriteTable.
while at it, also did some minor changes.

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