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

On Wed, Jan 25, 2023 at 3:15 AM Peter Smith <smithpb2250(at)gmail(dot)com> wrote:
>
> 1.
> @@ -210,7 +210,7 @@ int logical_decoding_work_mem;
> static const Size max_changes_in_memory = 4096; /* XXX for restore only */
>
> /* GUC variable */
> -int logical_decoding_mode = LOGICAL_DECODING_MODE_BUFFERED;
> +int logical_replication_mode = LOGICAL_REP_MODE_BUFFERED;
>
>
> I noticed that the comment /* GUC variable */ is currently only above
> the logical_replication_mode, but actually logical_decoding_work_mem
> is a GUC variable too. Maybe this should be rearranged somehow then
> change the comment "GUC variable" -> "GUC variables"?
>

I think moving these variables together doesn't sound like a good idea
because logical_decoding_work_mem variable is defined with other
related variable. Also, if we are doing the last comment, I think that
will obviate the need for this.

> ======
> src/backend/utils/misc/guc_tables.c
>
> @@ -4908,13 +4908,13 @@ struct config_enum ConfigureNamesEnum[] =
> },
>
> {
> - {"logical_decoding_mode", PGC_USERSET, DEVELOPER_OPTIONS,
> + {"logical_replication_mode", PGC_USERSET, DEVELOPER_OPTIONS,
> gettext_noop("Allows streaming or serializing each change in logical
> decoding."),
> NULL,
> GUC_NOT_IN_SAMPLE
> },
> - &logical_decoding_mode,
> - LOGICAL_DECODING_MODE_BUFFERED, logical_decoding_mode_options,
> + &logical_replication_mode,
> + LOGICAL_REP_MODE_BUFFERED, logical_replication_mode_options,
> NULL, NULL, NULL
> },
>
> That gettext_noop string seems incorrect. I think Kuroda-san
> previously reported the same, but then you replied it has been fixed
> already [1]
>
> > I felt the description seems not to be suitable for current behavior.
> > A short description should be like "Sets a behavior of logical replication", and
> > further descriptions can be added in lond description.
> I adjusted the description here.
>
> But this doesn't look fixed to me. (??)
>

Okay, so, how about the following for the 0001 patch:
short desc: Controls when to replicate each change.
long desc: On the publisher, it allows streaming or serializing each
change in logical decoding.

Then we can extend it as follows for the 0002 patch:
Controls when to replicate or apply each change
On the publisher, it allows streaming or serializing each change in
logical decoding. On the subscriber, it allows serialization of all
changes to files and notifies the parallel apply workers to read and
apply them at the end of the transaction.

> ======
> src/include/replication/reorderbuffer.h
>
> 3.
> @@ -18,14 +18,14 @@
> #include "utils/timestamp.h"
>
> extern PGDLLIMPORT int logical_decoding_work_mem;
> -extern PGDLLIMPORT int logical_decoding_mode;
> +extern PGDLLIMPORT int logical_replication_mode;
>
> Probably here should also be a comment to say "/* GUC variables */"
>

Okay, we can do this.

--
With Regards,
Amit Kapila.