Support COPY TO for partitioned tables.

Previously, COPY TO command didn't support directly specifying
partitioned tables so users had to use COPY (SELECT ...) TO variant.

This commit adds direct COPY TO support for partitioned
tables, improving both usability and performance. Performance tests
show it's faster than the COPY (SELECT ...) TO variant as it avoids
the overheads of query processing and sending results to the COPY TO
command.

When used with partitioned tables, COPY TO copies the same rows as
SELECT * FROM table. Row-level security policies of the partitioned
table are applied in the same way as when executing COPY TO on a plain
table.

Author: jian he <jian.universality@gmail.com>
Reviewed-by: vignesh C <vignesh21@gmail.com>
Reviewed-by: David Rowley <dgrowleyml@gmail.com>
Reviewed-by: Melih Mutlu <m.melihmutlu@gmail.com>
Reviewed-by: Kirill Reshke <reshkekirill@gmail.com>
Reviewed-by: Atsushi Torikoshi <torikoshia@oss.nttdata.com>
Reviewed-by: Álvaro Herrera <alvherre@kurilemu.de>
Reviewed-by: Masahiko Sawada <sawada.mshk@gmail.com>
Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Discussion: https://postgr.es/m/CACJufxEZt%2BG19Ors3bQUq-42-61__C%3Dy5k2wk%3DsHEFRusu7%3DiQ%40mail.gmail.com

1 files changed, 3 insertions, 0 deletions

diff --git a/src/test/regress/sql/rowsecurity.sql b/src/test/regress/sql/rowsecurity.sql
index 21ac0ca51ee..2d1be543391 100644
--- a/src/test/regress/sql/rowsecurity.sql
+++ b/src/test/regress/sql/rowsecurity.sql
@@ -362,16 +362,19 @@ SELECT * FROM pg_policies WHERE schemaname = 'regress_rls_schema' AND tablename
 SET SESSION AUTHORIZATION regress_rls_bob;
 SET row_security TO ON;
 SELECT * FROM part_document WHERE f_leak(dtitle) ORDER BY did;
+COPY part_document TO stdout WITH (DELIMITER ',');
 EXPLAIN (COSTS OFF) SELECT * FROM part_document WHERE f_leak(dtitle);
 
 -- viewpoint from regress_rls_carol
 SET SESSION AUTHORIZATION regress_rls_carol;
 SELECT * FROM part_document WHERE f_leak(dtitle) ORDER BY did;
+COPY part_document TO stdout WITH (DELIMITER ',');
 EXPLAIN (COSTS OFF) SELECT * FROM part_document WHERE f_leak(dtitle);
 
 -- viewpoint from regress_rls_dave
 SET SESSION AUTHORIZATION regress_rls_dave;
 SELECT * FROM part_document WHERE f_leak(dtitle) ORDER BY did;
+COPY part_document TO stdout WITH (DELIMITER ',');
 EXPLAIN (COSTS OFF) SELECT * FROM part_document WHERE f_leak(dtitle);
 
 -- pp1 ERROR