Re: speedup COPY TO for partitioned table.

On 2025-Jul-02, jian he wrote:

> @@ -673,11 +680,34 @@ BeginCopyTo(ParseState *pstate,
> errmsg("cannot copy from sequence \"%s\"",
> RelationGetRelationName(rel))));
> else if (rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
> - ereport(ERROR,
> - (errcode(ERRCODE_WRONG_OBJECT_TYPE),
> - errmsg("cannot copy from partitioned table \"%s\"",
> - RelationGetRelationName(rel)),
> - errhint("Try the COPY (SELECT ...) TO variant.")));
> + {
> + children = find_all_inheritors(RelationGetRelid(rel),
> + AccessShareLock,
> + NULL);
> +
> + foreach_oid(childreloid, children)
> + {
> + char relkind = get_rel_relkind(childreloid);
> +
> + if (relkind == RELKIND_FOREIGN_TABLE)
> + {
> + char *relation_name;
> +
> + relation_name = get_rel_name(childreloid);
> + ereport(ERROR,
> + errcode(ERRCODE_WRONG_OBJECT_TYPE),
> + errmsg("cannot copy from foreign table \"%s\"", relation_name),
> + errdetail("Partition \"%s\" is a foreign table in the partitioned table \"%s\"",
> + relation_name, RelationGetRelationName(rel)),
> + errhint("Try the COPY (SELECT ...) TO variant."));
> + }

This code looks like it's duplicating what you could obtain by using
RelationGetPartitionDesc and then observe the ->isleaf bits. Maybe have
a look at the function RelationHasForeignPartition() in the patch at
https://postgr.es/m/CANhcyEW_s2LD6RiDSMHtWQnpYB67EWXqf7N8mn7dOrnaKMfROg@mail.gmail.com
which looks very similar to what you need here. I think that would also
have the (maybe dubious) advantage that the rows will be output in
partition bound order rather than breadth-first (partition hierarchy)
OID order.

--
Álvaro Herrera 48°01'N 7°57'E — https://www.EnterpriseDB.com/
"The saddest aspect of life right now is that science gathers knowledge faster
than society gathers wisdom." (Isaac Asimov)