Re: speedup COPY TO for partitioned table.

On Sat, 29 Mar 2025 at 12:08, jian he <jian(dot)universality(at)gmail(dot)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