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From: Dmitry Koval <[email protected]>
To: Junwang Zhao <[email protected]>
Cc: [email protected]
Subject: Re: Add SPLIT PARTITION/MERGE PARTITIONS commands
Date: Wed, 11 Jun 2025 16:10:00 +0300
Message-ID: <[email protected]> (raw)
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Hi, Junwang Zhao!

Thank you for note.

1.
 >Would it be better to use RELATION_IS_OTHER_TEMP in this case?
 >I noticed that while other parts of tablecmds.c don’t use the macro,
 >all other files consistently use RELATION_IS_OTHER_TEMP.

Agreed, RELATION_IS_OTHER_TEMP is better. Changed.
The fix will be in the next patch.


2.
 >+/*
 >+* We intended to create the partition with the same persistence as the
 >+* parent table, but we still need to recheck because that might be
 >+* affected by the search_path.  If the parent is permanent, so must be
 >+* all of its partitions.
 >+*/

 >I have trouble understanding how this is possible, can you kindly
 >give me some guidance on this logic?

Perhaps this is best explained with an example.
(see src/test/regress/sql/partition_merge.sql).

(a) Create permanent table "t":

SET search_path = partitions_merge_schema, pg_temp, public;
CREATE TABLE t (i int) PARTITION BY RANGE (i);
CREATE TABLE tp_0_1 PARTITION OF t FOR VALUES FROM (0) TO (1);
CREATE TABLE tp_1_2 PARTITION OF t FOR VALUES FROM (1) TO (2);

(b) Attempt to merge persistent partitions tp_0_1, tp_1_2 into
temporary partition tp_0_2:

SET search_path = pg_temp, partitions_merge_schema, public;
-- Can't merge persistent partitions into a temporary partition
ALTER TABLE t MERGE PARTITIONS (tp_0_1, tp_1_2) INTO tp_0_2;

(c) "ALTER TABLE ... MERGE PARTITIONS ..." will return an error:

ERROR:  cannot create a temporary relation as partition of permanent 
relation "t"

-- 
With best regards,
Dmitry Koval

Postgres Professional: http://postgrespro.com

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