Re: Pgoutput not capturing the generated columns - Mailing list pgsql-hackers

On Tue, 4 Jun 2024 at 15:01, Peter Smith <smithpb2250@gmail.com> wrote:
>
> Hi,
>
> Here are some review comments for patch v5-0003.
>
> ======
> 0. Whitespace warnings when the patch was applied.
>
> [postgres@CentOS7-x64 oss_postgres_misc]$ git apply
> ../patches_misc/v5-0003-Support-copy-of-generated-columns-during-tablesyn.patch
> ../patches_misc/v5-0003-Support-copy-of-generated-columns-during-tablesyn.patch:29:
> trailing whitespace.
>           has no effect; the replicated data will be ignored and the subscriber
> ../patches_misc/v5-0003-Support-copy-of-generated-columns-during-tablesyn.patch:30:
> trailing whitespace.
>           column will be filled as normal with the subscriber-side computed or
> ../patches_misc/v5-0003-Support-copy-of-generated-columns-during-tablesyn.patch:189:
> trailing whitespace.
> (walrcv_server_version(LogRepWorkerWalRcvConn) >= 120000 &&
> warning: 3 lines add whitespace errors.
>
Fixed

> ======
> src/backend/commands/subscriptioncmds.c
>
> 1.
> - res = walrcv_exec(wrconn, cmd.data, check_columnlist ? 3 : 2, tableRow);
> + column_count = (!include_generated_column && check_gen_col) ? 4 :
> (check_columnlist ? 3 : 2);
> + res = walrcv_exec(wrconn, cmd.data, column_count, tableRow);
>
> The 'column_count' seems out of control. Won't it be far simpler to
> assign/increment the value dynamically only as required instead of the
> tricky calculation at the end which is unnecessarily difficult to
> understand?
>
I have removed this piece of code.

> ~~~
>
> 2.
> + /*
> + * If include_generated_column option is false and all the column of
> the table in the
> + * publication are generated then we should throw an error.
> + */
> + if (!isnull && !include_generated_column && check_gen_col)
> + {
> + attlist = DatumGetArrayTypeP(attlistdatum);
> + gen_col_count = DatumGetInt32(slot_getattr(slot, 4, &isnull));
> + Assert(!isnull);
> +
> + attcount = ArrayGetNItems(ARR_NDIM(attlist), ARR_DIMS(attlist));
> +
> + if (attcount != 0 && attcount == gen_col_count)
> + ereport(ERROR,
> + errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
> + errmsg("cannot use only generated column for table \"%s.%s\" in
> publication when generated_column option is false",
> +    nspname, relname));
> + }
> +
>
> Why do you think this new logic/error is necessary?
>
> IIUC the 'include_generated_columns' should be false to match the
> existing HEAD behavior. So this scenario where your publisher-side
> table *only* has generated columns is something that could already
> happen, right? IOW, this introduced error could be a candidate for
> another discussion/thread/patch, but is it really required for this
> current patch?
>
Yes, this scenario can also happen in HEAD. For this patch I have
removed this check.

> ======
> src/backend/replication/logical/tablesync.c
>
> 3.
>   lrel->remoteid,
> - (walrcv_server_version(LogRepWorkerWalRcvConn) >= 120000 ?
> -   "AND a.attgenerated = ''" : ""),
> + (walrcv_server_version(LogRepWorkerWalRcvConn) >= 120000 &&
> + (walrcv_server_version(LogRepWorkerWalRcvConn) <= 160000 ||
> + !MySubscription->includegeneratedcolumn) ? "AND a.attgenerated = ''" : ""),
>
> This ternary within one big appendStringInfo seems quite complicated.
> Won't it be better to split the appendStringInfo into multiple parts
> so the generated-cols calculation can be done more simply?
>
Fixed

> ======
> src/test/subscription/t/011_generated.pl
>
> 4.
> I think there should be a variety of different tablesync scenarios
> (when 'include_generated_columns' is true) tested here instead of just
> one, and all varieties with lots of comments to say what they are
> doing, expectations etc.
>
> a. publisher-side gen-col "a" replicating to subscriber-side NOT
> gen-col "a" (ok, value gets replicated)
> b. publisher-side gen-col "a" replicating to subscriber-side gen-col
> (ok, but ignored)
> c. publisher-side NOT gen-col "b" replicating to subscriber-side
> gen-col "b" (error?)
>
Added the tests

> ~~
>
> 5.
> +$result = $node_subscriber->safe_psql('postgres', "SELECT a, b FROM tab3");
> +is( $result, qq(1|2
> +2|4
> +3|6), 'generated columns initial sync with include_generated_column = true');
>
> Should this say "ORDER BY..." so it will not fail if the row order
> happens to be something unanticipated?
>
Fixed

> ======
>
> 99.
> Also, see the attached file with numerous other nitpicks:
> - plural param- and var-names
> - typos in comments
> - missing spaces
> - SQL keyword should be UPPERCASE
> - etc.
>
> Please apply any/all of these if you agree with them.
Fixed

Patch 7-0002 contains all the changes. Please refer [1]
[1]: https://www.postgresql.org/message-id/CANhcyEUz0FcyR3T76b%2BNhtmvWO7o96O_oEwsLZNZksEoPmVzXw%40mail.gmail.com

Thanks and Regards,
Shlok Kyal