From: Tom Lane <tgl@sss.pgh.pa.us>
To: "James Pang (chaolpan)" <chaolpan@cisco.com>
cc: "pgsql-admin@lists.postgresql.org" <pgsql-admin@lists.postgresql.org>
Subject: Re: multiple sessions to create index in parallel support
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Comments: In-reply-to "James Pang (chaolpan)" <chaolpan@cisco.com>
	message dated "Tue, 21 Jun 2022 10:18:20 -0000"
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Date: Tue, 21 Jun 2022 10:30:01 -0400
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"James Pang (chaolpan)" <chaolpan@cisco.com> writes:
>    We have a large database that just migrated data from Oracle to Postg=
res(13.4), after data load. We try to create indexes ,  with only one conn=
ection , the create index automatically run in parallel (table size 40G) ,=
  then we started two connections and each session creating index on large=
 table, but at this time, only 1 session parallel creating index, the othe=
r one creating index in serial. There are enough parallel_workers and memo=
ry.  Is that expected ?  only 1 session allowed to parallel index creating=
 at the same time ?

Check your settings for max_parallel_workers and
max_parallel_maintenance_workers.

			regards, tom lane