Re: speedup COPY TO for partitioned table.

On Sat, 29 Mar 2025 at 12:08, jian he <jian.universality@gmail.com> wrote:
>
>
> I consolidated it into a new function: CopyThisRelTo.

Few comments:
1) Here the error message is not correct, we are printing the original
table from where copy was done which is a regular table and not a
foreign table, we should use childreloid instead of rel.

+                               if (relkind == RELKIND_FOREIGN_TABLE)
+                                       ereport(ERROR,
+
errcode(ERRCODE_WRONG_OBJECT_TYPE),
+                                                       errmsg("cannot
copy from foreign table \"%s\"",
+
 RelationGetRelationName(rel)),
+
errdetail("partition \"%s\" is a foreign table",
RelationGetRelationName(rel)),
+                                                       errhint("Try
the COPY (SELECT ...) TO variant."));

In the error detail you can include the original table too.

postgres=# copy t1 to stdout(header);
ERROR:  cannot copy from foreign table "t1"
DETAIL:  partition "t1" is a foreign table
HINT:  Try the COPY (SELECT ...) TO variant.

2) 2.a) I felt the comment should be "then copy partitioned rel to
destionation":
+ * rel: the relation to be copied to.
+ * root_rel: if not null, then the COPY TO partitioned rel.
+ * processed: number of tuple processed.
+*/
+static void
+CopyThisRelTo(CopyToState cstate, Relation rel, Relation root_rel,
uint64 *processed)
+{
+       TupleTableSlot *slot;

2.b) you can have processed argument in the next line for better readability

3) There is a small indentation issue here:
+       /*
+        * partition's rowtype might differ from the root table's.  We must
+        * convert it back to the root table's rowtype as we are export
+        * partitioned table data here.
+       */
+       if (root_rel != NULL)

Regards,
Vignesh