On Mon, 6 Jan 2025 at 08:47, Peter Smith <smithpb2...@gmail.com> wrote:
>
> Hi Vignesh,
>
> Some review comments for your v2 patch.
>
> ======
> doc/src/sgml/logical-replication.sgml
>
> AFAICT the only difference you made is changing:
> FROM "a special kind of apply process"
> TO "a special kind of table synchronization worker process".
>
> There is only ONE kind of tablesync process, so I think saying "a
> special kind of table synchronization worker process" seems
> misleading. I also thought maybe it is better to mention that this is
> PER table.
>
> SUGGESTION:
> ... a special table synchronization worker process per table.
Thanks, the updated v3 version patch has the changes for the same.
Regards,
Vignesh
From 292f8d0249b2b1772d2cff6ae1208954eb188b7f Mon Sep 17 00:00:00 2001
From: Vignesh <vignes...@gmail.com>
Date: Mon, 13 Jan 2025 12:27:55 +0530
Subject: [PATCH v3] Improve documentation on table synchronization worker
process
Update the documentation to explain the process of initial data
replication using the table synchronization worker. Also, clarify
how the worker process is automatically respawned in the event of
failure, based on the configuration of the wal_retrieve_retry_interval
parameter guc.
---
doc/src/sgml/config.sgml | 3 ++-
doc/src/sgml/logical-replication.sgml | 33 +++++++++++++++++----------
2 files changed, 23 insertions(+), 13 deletions(-)
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 3f41a17b1f..e063598879 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4953,7 +4953,8 @@ ANY <replaceable class="parameter">num_sync</replaceable> ( <replaceable class="
</para>
<para>
In logical replication, this parameter also limits how often a failing
- replication apply worker will be respawned.
+ replication apply worker or table synchronization worker will be
+ respawned.
</para>
</listitem>
</varlistentry>
diff --git a/doc/src/sgml/logical-replication.sgml b/doc/src/sgml/logical-replication.sgml
index 8290cd1a08..86aea348f1 100644
--- a/doc/src/sgml/logical-replication.sgml
+++ b/doc/src/sgml/logical-replication.sgml
@@ -1993,18 +1993,18 @@ CONTEXT: processing remote data for replication origin "pg_16395" during "INSER
<title>Initial Snapshot</title>
<para>
The initial data in existing subscribed tables are snapshotted and
- copied in a parallel instance of a special kind of apply process.
- This process will create its own replication slot and copy the existing
- data. As soon as the copy is finished the table contents will become
- visible to other backends. Once existing data is copied, the worker
- enters synchronization mode, which ensures that the table is brought
- up to a synchronized state with the main apply process by streaming
- any changes that happened during the initial data copy using standard
- logical replication. During this synchronization phase, the changes
- are applied and committed in the same order as they happened on the
- publisher. Once synchronization is done, control of the
- replication of the table is given back to the main apply process where
- replication continues as normal.
+ copied in a parallel instance of a special table synchronization
+ worker process per table. This process will create its own replication
+ slot and copy the existing data. As soon as the copy is finished the
+ table contents will become visible to other backends. Once existing data
+ is copied, the worker enters synchronization mode, which ensures that the
+ table is brought up to a synchronized state with the main apply process by
+ streaming any changes that happened during the initial data copy using
+ standard logical replication. During this synchronization phase, the
+ changes are applied and committed in the same order as they happened on
+ the publisher. Once synchronization is done, control of the replication
+ of the table is given back to the main apply process where replication
+ continues as normal.
</para>
<note>
<para>
@@ -2015,6 +2015,15 @@ CONTEXT: processing remote data for replication origin "pg_16395" during "INSER
when copying the existing table data.
</para>
</note>
+ <note>
+ <para>
+ If a table synchronization worker fails during copy, the apply worker
+ detects the failure and respawns the table synchronization worker to
+ continue the synchronization process. This behaviour ensures that
+ transient errors do not permanently disrupt the replication setup. See
+ also <link linkend="guc-wal-retrieve-retry-interval"><varname>wal_retrieve_retry_interval</varname></link>.
+ </para>
+ </note>
</sect2>
</sect1>
--
2.43.0
