RE: Logical Replication of sequences

[Hayato Kuroda (Fujitsu)]

Dear Vignesh,

Thanks for updating the patch. Here are my small comments:

01.
Per pgindent report, publicationcmds.c should be fixed.

02.
```
+       ScanKeyInit(&skey[1],
+                               Anum_pg_subscription_rel_srsubstate,
+                               BTEqualStrategyNumber, F_CHARNE,
+                               CharGetDatum(SUBREL_STATE_READY));
```

I felt it is more natural to "srsubstate = 'i'", instead of "srsubstate <> 'r'"

03.
```
+               table_close(sequence_rel, NoLock);
+       }
+
+       /* Cleanup */
+       systable_endscan(scan);
+       table_close(rel, AccessShareLock);
+
+       CommitTransactionCommand();
```

To clarify, can we release the sequence at the end of the inner loop?

I found that sequence relation is closed (but not release the lock) then commit
the transaction once. This approach cannot avoid dropping it by concurrent
transactions, but maybe you did due to the performance reason. So...I felt we
may able to release bit earlier.

04.
```
+                       sequence_rel = try_table_open(seqinfo->localrelid, 
RowExclusiveLock);
+
+                       /* Get the local sequence */
+                       tup = SearchSysCache1(SEQRELID, 
ObjectIdGetDatum(seqinfo->localrelid));
+                       if (!sequence_rel || !HeapTupleIsValid(tup))
+                       {
+                               elog(LOG, "skip synchronization of sequence 
\"%s.%s\" because it has been dropped concurrently",
+                                        seqinfo->nspname, seqinfo->seqname);
+
+                               batch_skipped_count++;
+                               continue;
+                       }
```

a. Code comment can be atop try_table_open().
b. Isn't it enough to check HeapTupleIsValid() here?

05.
```
+                       /* Update the sequence only if the parameters are 
identical */
+                       if (seqform->seqtypid == seqtypid &&
+                               seqform->seqmin == seqmin && seqform->seqmax == 
seqmax &&
+                               seqform->seqcycle == seqcycle &&
+                               seqform->seqstart == seqstart &&
+                               seqform->seqincrement == seqincrement)
```

I noticed that seqcache is not compared. Is there a reason?

06.
```
+       foreach_ptr(LogicalRepSequenceInfo, seq_info, sequences_to_copy)
+       {
+               pfree(seq_info->seqname);
+               pfree(seq_info->nspname);
+               pfree(seq_info);
+       }
```

Per comment atop foreach_delete_current(), we should not directly do pfree()
the entry. Can you use foreach_delete_current()? I.e.,

07.
```
        foreach_ptr(LogicalRepSequenceInfo, seq_info, sequences_to_copy)
        {
                pfree(seq_info->seqname);
                pfree(seq_info->nspname);
                
                sequences_to_copy =
                        foreach_delete_current(sequences_to_copy, seq_info);
        }
```

08.
```
+$node_subscriber->init(allows_streaming => 'logical');
```

Actually no need to set to 'logical'.


Best regards,
Hayato Kuroda
FUJITSU LIMITED