Re: Perform streaming logical transactions by background workers and parallel apply

Peter Smith <smithpb2250@gmail.com>

From: Peter Smith <smithpb2250@gmail.com>

To: Amit Kapila <amit.kapila16@gmail.com>

Cc: "houzj.fnst@fujitsu.com" <houzj.fnst@fujitsu.com>, Masahiko Sawada <sawada.mshk@gmail.com>, shveta malik <shveta.malik@gmail.com>, "wangw.fnst@fujitsu.com" <wangw.fnst@fujitsu.com>, "shiy.fnst@fujitsu.com" <shiy.fnst@fujitsu.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Dilip Kumar <dilipbalaut@gmail.com>

Date: 2023-02-01T23:22:06Z

Lists: pgsql-hackers

Some minor review comments for v91-0001

======
doc/src/sgml/config.sgml

1.
        <para>
-        Allows streaming or serializing changes immediately in
logical decoding.
-        The allowed values of <varname>logical_replication_mode</varname> are
-        <literal>buffered</literal> and <literal>immediate</literal>. When set
-        to <literal>immediate</literal>, stream each change if
+        The allowed values are <literal>buffered</literal> and
+        <literal>immediate</literal>. The default is
<literal>buffered</literal>.
+        This parameter is intended to be used to test logical decoding and
+        replication of large transactions for which otherwise we need
to generate
+        the changes till <varname>logical_decoding_work_mem</varname> is
+        reached.  The effect of <varname>logical_replication_mode</varname> is
+        different for the publisher and subscriber:
+       </para>

The "for which otherwise..." part is only relevant for the
publisher-side. So it seemed slightly strange to give the reason why
to use the GUC for one side but not the other side.

Maybe we can just to remove that "for which otherwise..." part, since
the logical_decoding_work_mem gets mentioned later in the "On the
publisher side,..." paragraph anyway.

~~~

2.
        <para>
-        This parameter is intended to be used to test logical decoding and
-        replication of large transactions for which otherwise we need to
-        generate the changes till <varname>logical_decoding_work_mem</varname>
-        is reached.
+        On the subscriber side, if the <literal>streaming</literal>
option is set to
+        <literal>parallel</literal>,
<varname>logical_replication_mode</varname>
+        can be used to direct the leader apply worker to send changes to the
+        shared memory queue or to serialize changes to the file.  When set to
+        <literal>buffered</literal>, the leader sends changes to parallel apply
+        workers via a shared memory queue.  When set to
+        <literal>immediate</literal>, the leader serializes all
changes to files
+        and notifies the parallel apply workers to read and apply them at the
+        end of the transaction.
        </para>

"or serialize changes to the file." --> "or serialize all changes to
files." (just to use same wording as later in this same paragraph, and
also same wording as the GUC hint text).

------
Kind Regards,
Peter Smith.
Fujitsu Australia

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

Fix invalid memory access during the shutdown of the parallel apply worker.
- 3d144c6c8602 16.0 landed
Fix assertion failure in apply worker.
- de63f8dadee4 16.0 landed
Use elog to report unexpected action in handle_streamed_transaction().
- 781ac42d43ab 16.0 landed
Use appropriate wait event when sending data in the apply worker.
- d9d7fe68d35e 16.0 landed
Allow the logical_replication_mode to be used on the subscriber.
- 9f2213a7c575 16.0 landed
Rename GUC logical_decoding_mode to logical_replication_mode.
- 1e8b61735cfb 16.0 landed
Display the leader apply worker's PID for parallel apply workers.
- d540a02a724b 16.0 landed
Improve the code to decide and process the apply action.
- c981d9145dea 16.0 landed
Document the newly added wait events added by commit 216a784829.
- cd06ccd78fcf 16.0 landed
Perform apply of large transactions by parallel workers.
- 216a784829c2 16.0 landed
Wake up a subscription's replication worker processes after DDL.
- c6e1f62e2cee 16.0 cited
Add copyright notices to meson files
- 8284cf5f746f 16.0 cited
Better document logical replication parameters
- a8500750ca0a 16.0 cited
Add a common function to generate the origin name.
- 776e1c8a5d14 16.0 cited
Harmonize parameter names in storage and AM code.
- bfcf1b34805f 16.0 cited
Avoid using list_length() to test for empty list.
- efd0c16becbf 16.0 cited
Improve two comments related to a boolean DefElem's value
- 8445f5a21d40 16.0 cited
Fix partition table's REPLICA IDENTITY checking on the subscriber.
- 26b3455afaa9 15.0 cited
Fix data inconsistency between publisher and subscriber.
- b7658c24c7c1 15.0 cited
Fix cache look-up failures while applying changes in logical replication.
- 5a97b1325453 15.0 cited