Re: row filtering for logical replication

On Wed, Jan 12, 2022 at 7:19 PM houzj.fnst@fujitsu.com
<houzj.fnst@fujitsu.com> wrote:
>
> On Wed, Jan 12, 2022 5:38 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> Attach the v63 patch set which include the following changes.
>

Few comments:
=============
1.
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+      <structfield>prqual</structfield> <type>pg_node_tree</type>
+      </para>
+      <para>Expression tree (in <function>nodeToString()</function>
+      representation) for the relation's qualifying condition</para></entry>
+     </row>

Let's slightly modify this as: "Expression tree (in
<function>nodeToString()</function> representation) for the relation's
qualifying condition. Null if there is no qualifying condition."

2.
+   A <literal>WHERE</literal> clause allows simple expressions. The simple
+   expression cannot contain any aggregate or window functions, non-immutable
+   functions, user-defined types, operators or functions.

This part in the docs should be updated to say something similar to
what we have in the commit message for this part or maybe additionally
in some way we can say which other forms of expressions are not
allowed.

3.
+   for which the <replaceable
class="parameter">expression</replaceable> returns
+   false or null will not be published.
+   If the subscription has several publications in which
+   the same table has been published with different <literal>WHERE</literal>

In the above text line spacing appears a bit odd to me. There doesn't
seem to be a need for extra space after line-2 and line-3 in
above-quoted text.

4.
/*
+ * Return the relid of the topmost ancestor that is published via this

We normally seem to use Returns in similar places.

5.
+ * The simple expression contains the following restrictions:
+ * - User-defined operators are not allowed;
+ * - User-defined functions are not allowed;
+ * - User-defined types are not allowed;
+ * - Non-immutable built-in functions are not allowed;
+ * - System columns are not allowed.

Why system columns are not allowed in the above context?

6.
+static void
+transformPubWhereClauses(List *tables, const char *queryString)

To keep the function naming similar to other nearby functions, it is
better to name this as TransformPubWhereClauses.

7. In AlterPublicationTables(), won't it better if we
transformPubWhereClauses() after
CheckObjSchemaNotAlreadyInPublication() to avoid extra processing in
case of errors.

8.
+ /*
+ * Check if the relation is member of the existing schema in the
+ * publication or member of the schema list specified.
+ */
  CheckObjSchemaNotAlreadyInPublication(rels, schemaidlist,
    PUBLICATIONOBJ_TABLE);

I don't see the above comment addition has anything to do with this
patch. Can we remove it?

9.
 CheckCmdReplicaIdentity(Relation rel, CmdType cmd)
 {
  PublicationActions *pubactions;
+ AttrNumber bad_rfcolnum;

  /* We only need to do checks for UPDATE and DELETE. */
  if (cmd != CMD_UPDATE && cmd != CMD_DELETE)
  return;

+ if (rel->rd_rel->relreplident == REPLICA_IDENTITY_FULL)
+ return;
+
+ /*
+ * It is only safe to execute UPDATE/DELETE when all columns referenced in
+ * the row filters from publications which the relation is in are valid -
+ * i.e. when all referenced columns are part of REPLICA IDENTITY, or the
+ * table does not publish UPDATES or DELETES.
+ */
+ bad_rfcolnum = GetRelationPublicationInfo(rel, true);

Can we name this variable as invalid_rf_column?

-- 
With Regards,
Amit Kapila.