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

On Mon, Jan 30, 2023 at 3:23 PM houzj(dot)fnst(at)fujitsu(dot)com
<houzj(dot)fnst(at)fujitsu(dot)com> wrote:
>
> On Monday, January 30, 2023 12:13 PM Peter Smith <smithpb2250(at)gmail(dot)com> wrote:
> >
> > Here are my review comments for v88-0002.
>
> Thanks for your comments.
>
> >
> > ======
> > 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.
>
> We have tests that check the ereport ERROR and ereport WARNING message(by
> search for the ERROR or WARNING keyword for all the tap tests), so I think
> checking the LOG should be fine.
>
> > ======
> > 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"
>
> Changed.
>
> > ~~~
> >
> > 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.
>
> Changed.
>
> > ======
> > 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.
> >
>
> Changed.
>
> Attach the new version patch which addressed all comments so far (the v88-0001
> has been committed, so we only have one remaining patch this time).
>

I have one comment on v89 patch:

+ /*
+ * Using 'immediate' mode returns false to cause a switch to
+ * PARTIAL_SERIALIZE mode so that the remaining changes will
be serialized.
+ */
+ if (logical_replication_mode == LOGICAL_REP_MODE_IMMEDIATE)
+ return false;
+

Probably we might want to add unlikely() here since we could pass
through this path very frequently?

The rest looks good to me.

Regards,

--
Masahiko Sawada
Amazon Web Services: https://aws.amazon.com