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

Here are my review comments for v88-0002.

======
General

1.
The test cases are checking the log content but they are not checking
for debug logs or untranslated elogs -- they are expecting a normal
ereport LOG that might be translated. I’m not sure if that is OK, or
if it is a potential problem.

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

2.
On the publisher side, logical_replication_mode allows allows
streaming or serializing changes immediately in logical decoding. When
set to immediate, stream each change if streaming option (see optional
parameters set by CREATE SUBSCRIPTION) is enabled, otherwise,
serialize each change. When set to buffered, the decoding will stream
or serialize changes when logical_decoding_work_mem is reached.

2a.
typo "allows allows"  (Kuroda-san reported same)

2b.
"if streaming option" --> "if the streaming option"

~~~

3.
On the subscriber side, if streaming option is set to parallel,
logical_replication_mode also allows the leader apply worker to send
changes to the shared memory queue or to serialize changes.

SUGGESTION
On the subscriber side, if the streaming option is set to parallel,
logical_replication_mode can be used to direct the leader apply worker
to send changes to the shared memory queue or to serialize changes.

======
src/backend/utils/misc/guc_tables.c

4.
  {
  {"logical_replication_mode", PGC_USERSET, DEVELOPER_OPTIONS,
- gettext_noop("Controls when to replicate each change."),
- gettext_noop("On the publisher, it allows streaming or serializing
each change in logical decoding."),
+ gettext_noop("Controls the internal behavior of logical replication
publisher and subscriber"),
+ gettext_noop("On the publisher, it allows streaming or "
+ "serializing each change in logical decoding. On the "
+ "subscriber, in parallel streaming mode, it allows "
+ "the leader apply worker to serialize changes to "
+ "files and notifies the parallel apply workers to "
+ "read and apply them at the end of the transaction."),
  GUC_NOT_IN_SAMPLE
  },
Suggest re-wording the long description (subscriber part) to be more
like the documentation text.

BEFORE
On the subscriber, in parallel streaming mode, it allows the leader
apply worker to serialize changes to files and notifies the parallel
apply workers to read and apply them at the end of the transaction.

SUGGESTION
On the subscriber, if the streaming option is set to parallel, it
directs the leader apply worker to send changes to the shared memory
queue or to serialize changes and apply them at the end of the
transaction.

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Kind Regards,
Peter Smith.
Fujitsu Australia