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

On Fri, 16 Aug 2024 at 10:04, Shubham Khanna
<khannashubham1197@gmail.com> wrote:
>
> On Thu, Aug 8, 2024 at 12:43 PM Peter Smith <smithpb2250@gmail.com> wrote:
> >
> > Hi Shubham,
> >
> > I think the v25-0001 patch only half-fixes the problems reported in my
> > v24-0001 review.
> >
> > ~
> >
> > Background (from the commit message):
> > This commit enables support for the 'include_generated_columns' option
> > in logical replication, allowing the transmission of generated column
> > information and data alongside regular table changes.
> >
> > ~
> >
> > The broken TAP test scenario in question is replicating from a
> > "not-generated" column to a "generated" column. As the generated
> > column is not on the publishing side, IMO the
> > 'include_generated_columns' option should have zero effect here.
> >
> > In other words, I expect this TAP test for 'include_generated_columns
> > = true' case should also be failing, as I wrote already yesterday:
> >
> > +# FIXME
> > +# Since there is no generated column on the publishing side this should give
> > +# the same result as the previous test. -- e.g. something like:
> > +# ERROR:  logical replication target relation
> > "public.tab_nogen_to_gen" is missing
> > +# replicated column: "b"
>
> I have fixed the given comments. The attached v26-0001 Patch contains
> the required changes.

Few comments:
1) There's no need to pass include_generated_columns in this case; we
can retrieve it from ctx->data instead:
@@ -749,7 +764,7 @@ maybe_send_schema(LogicalDecodingContext *ctx,
 static void
 send_relation_and_attrs(Relation relation, TransactionId xid,
                                                LogicalDecodingContext *ctx,
-                                               Bitmapset *columns)
+                                               Bitmapset *columns,
bool include_generated_columns)
 {
        TupleDesc       desc = RelationGetDescr(relation);
        int                     i;
@@ -766,7 +781,10 @@ send_relation_and_attrs(Relation relation,
TransactionId xid,

2) Commit message:
If the subscriber-side column is also a generated column then this option
has no effect; the replicated data will be ignored and the subscriber
column will be filled as normal with the subscriber-side computed or
default data.

An error will occur in this case, so the message should be updated accordingly.

3) The current test is structured as follows: a) Create all required
tables b) Insert data into tables c) Create publications d) Create
subscriptions e) Perform inserts and verify
This approach can make reviewing and maintenance somewhat challenging.

Instead, could you modify it to: a) Create the required table for a
single test b) Insert data for this test c) Create the publication for
this test d) Create the subscriptions for this test e) Perform inserts
and verify f) Clean up

4) We can maintain the test as a separate 0002 patch, as it may need a
few rounds of review and final adjustments. Once it's fully completed,
we can merge it back in.

5) Once we create and drop publication/subscriptions for individual
tests, we won't need such extensive configuration; we should be able
to run them with default values:
+$node_publisher->append_conf(
+       'postgresql.conf',
+       "max_wal_senders = 20
+        max_replication_slots = 20");

Regards,
Vignesh