Re: row filtering for logical replication

On Wed, Mar 31, 2021 at 7:17 AM Euler Taveira <euler(at)eulerto(dot)com> wrote:
>
> On Tue, Mar 30, 2021, at 8:23 AM, Amit Kapila wrote:
>
> On Mon, Mar 29, 2021 at 6:47 PM Euler Taveira <euler(at)eulerto(dot)com> wrote:
> >
> Few comments:
> ==============
> 1. How can we specify row filters for multiple tables for a
> publication? Consider a case as below:
>
> It is not possible. Row filter is a per table option. Isn't it clear from the
> synopsis?
>

Sorry, it seems I didn't read it properly earlier, now I got it.

>
> 2.
> + /*
> + * Although ALTER PUBLICATION grammar allows WHERE clause to be specified
> + * for DROP TABLE action, it doesn't make sense to allow it. We implement
> + * this restriction here, instead of complicating the grammar to enforce
> + * it.
> + */
> + if (stmt->tableAction == DEFELEM_DROP)
> + {
> + ListCell *lc;
> +
> + foreach(lc, stmt->tables)
> + {
> + PublicationTable *t = lfirst(lc);
> +
> + if (t->whereClause)
> + ereport(ERROR,
> + (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
> + errmsg("cannot use a WHERE clause when removing table from
> publication \"%s\"",
> + NameStr(pubform->pubname))));
> + }
> + }
>
> Is there a reason to deal with this here separately rather than in the
> ALTER PUBLICATION grammar?
>
> Good question. IIRC the issue is that AlterPublicationStmt->tables has a list
> element that was a relation_expr_list and was converted to
> publication_table_list. If we share 'tables' with relation_expr_list (for ALTER
> PUBLICATION ... DROP TABLE) and publication_table_list (for the other ALTER
> PUBLICATION ... ADD|SET TABLE), the OpenTableList() has to know what list
> element it is dealing with. I think I came to the conclusion that it is less
> uglier to avoid changing OpenTableList() and CloseTableList().
>
> [Doing some experimentation...]
>
> Here is a patch that remove the referred code.
>

Thanks, few more comments:
1. In pgoutput_change, we are always sending schema even though we
don't send actual data because of row filters. It may not be a problem
in many cases but I guess for some odd cases we can avoid sending
extra information.

2. In get_rel_sync_entry(), we are caching the qual for rel_sync_entry
even though we won't publish it which seems unnecessary?

3.
@@ -1193,5 +1365,11 @@ rel_sync_cache_publication_cb(Datum arg, int
cacheid, uint32 hashvalue)
entry->pubactions.pubupdate = false;
entry->pubactions.pubdelete = false;
entry->pubactions.pubtruncate = false;
+
+ if (entry->qual != NIL)
+ list_free_deep(entry->qual);

Seeing one previous comment in this thread [1], I am wondering if
list_free_deep is enough here?

4. Can we write explicitly in the docs that row filters won't apply
for Truncate operation?

5. Getting some whitespace errors:
git am /d/PostgreSQL/Patches/logical_replication/row_filter/v14-0001-Row-filter-for-logical-replication.patch
.git/rebase-apply/patch:487: trailing whitespace.

warning: 1 line adds whitespace errors.
Applying: Row filter for logical replication

[1] - https://www.postgresql.org/message-id/20181123161933.jpepibtyayflz2xg%40alvherre.pgsql

--
With Regards,
Amit Kapila.