Horton

Re: row filtering for logical replication

Dilip Kumar <dilipbalaut@gmail.com>

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From: Dilip Kumar <dilipbalaut@gmail.com>
To: Ajin Cherian <itsajin@gmail.com>
Cc: Peter Smith <smithpb2250@gmail.com>, "houzj.fnst@fujitsu.com" <houzj.fnst@fujitsu.com>, Greg Nancarrow <gregn4422@gmail.com>, Euler Taveira <euler@eulerto.com>, Rahila Syed <rahilasyed90@gmail.com>, Peter Eisentraut <peter.eisentraut@enterprisedb.com>, Önder Kalacı <onderkalaci@gmail.com>, japin <japinli@hotmail.com>, Michael Paquier <michael@paquier.xyz>, David Steele <david@pgmasters.net>, Craig Ringer <craig@2ndquadrant.com>, Amit Kapila <amit.kapila16@gmail.com>, Amit Langote <amitlangote09@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2021-11-15T09:14:24Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Release cache tuple when no longer needed

  2. Add some additional tests for row filters in logical replication.

  3. Fix one of the tests introduced in commit 52e4f0cd47.

  4. Allow specifying row filters for logical replication of tables.

  5. Move scanint8() to numutils.c

  6. Replace Test::More plans with done_testing

  7. Reduce relcache access in WAL sender streaming logical changes

  8. Small cleanups related to PUBLICATION framework code

  9. Add a view to show the stats of subscription workers.

  10. Allow publishing the tables of schema.

  11. Doc: improve documentation of CREATE/ALTER SUBSCRIPTION.

  12. Add PublicationTable and PublicationRelInfo structs

  13. Remove unused argument "txn" in maybe_send_schema().

  14. Add prepare API support for streaming transactions in logical replication.

  15. Unify PostgresNode's new() and get_new_node() methods

  16. Use l*_node() family of functions where appropriate

  17. Add support for prepared transactions to built-in logical replication.

  18. Restore the portal-level snapshot after procedure COMMIT/ROLLBACK.

  19. Rename a parse node to be more general

  20. Remove unused column atttypmod from initial tablesync query

  21. SEARCH and CYCLE clauses

On Fri, Nov 12, 2021 at 3:49 PM Ajin Cherian <itsajin@gmail.com> wrote:
>
> Attaching version 39-
>

Some comments on 0006

--
 /*
+ * Write UPDATE to the output stream using cached virtual slots.
+ * Cached updates will have both old tuple and new tuple.
+ */
+void
+logicalrep_write_update_cached(StringInfo out, TransactionId xid, Relation rel,
+                TupleTableSlot *oldtuple, TupleTableSlot *newtuple,
bool binary)
+{


Function, logicalrep_write_update_cached is exactly the same as
logicalrep_write_update, except calling logicalrep_write_tuple_cached
vs logicalrep_write_tuple.  So I don't like the idea of making
complete duplicate copies. instead either we can keep a if check or we
can pass this logicalrep_write_tuple(_cached) as a function pointer.

--

Looking further, I realized that "logicalrep_write_tuple" and
"logicalrep_write_tuple_cached" are completely duplicate except first
one is calling "heap_deform_tuple" and then using local values[] array
and the second one is directly using the slot->values[] array, so in
fact we can pass this also as a parameter or we can put just one if
check the populate the values[] and null array, so if it is cached we
will point directly to the slot->values[] otherwise
heap_deform_tuple(), I think this should be just one simple check.
--
+
+/*
+ * Change is checked against the row filter, if any.
+ *
+ * If it returns true, the change is replicated, otherwise, it is not.
+ */
+static bool
+pgoutput_row_filter_virtual(Relation relation, TupleTableSlot *slot,
RelationSyncEntry *entry)

IMHO, the comments should explain how it is different from the
pgoutput_row_filter function.  Also comments are saying "If it returns
true, the change is replicated, otherwise, it is not" which is not
exactly true for this function, I mean based on that the caller will
change the action.  So I think it is enough to say what this function
is doing but not required to say what the caller will do based on what
this function returns.


--

+    for (i = 0; i < desc->natts; i++)
+    {
+        Form_pg_attribute att = TupleDescAttr(desc, i);
+
+        /* if the column in the new_tuple is null, nothing to do */
+        if (tmp_new_slot->tts_isnull[i])
+            continue;

Put some comments over this loop about what it is trying to do, and
overall I think there are not sufficient comments in the
pgoutput_row_filter_update_check function.

--
+        /*
+          * Unchanged toasted replica identity columns are
+          * only detoasted in the old tuple, copy this over to the newtuple.
+          */
+        if ((att->attlen == -1 &&
VARATT_IS_EXTERNAL_ONDISK(tmp_new_slot->tts_values[i])) &&
+                (!old_slot->tts_isnull[i] &&
+                    !(VARATT_IS_EXTERNAL_ONDISK(old_slot->tts_values[i]))))

Is it ever possible that if the attribute is not NULL in the old slot
still it is stored as VARATT_IS_EXTERNAL_ONDISK? I think no, so
instead of adding
this last condition in check it should be asserted inside the if check.

--
 static bool
-pgoutput_row_filter(PGOutputData *data, Relation relation, HeapTuple
oldtuple, HeapTuple newtuple, RelationSyncEntry *entry)
+pgoutput_row_filter_update_check(Relation relation, HeapTuple
oldtuple, HeapTuple newtuple, RelationSyncEntry *entry,
ReorderBufferChangeType *action)
+{

This function definition header is too long to fit in one line, so
better to break it.  I think running will be a good idea.


-- 
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com