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

contrib/postgres_fdw/expected/postgres_fdw.out

@@ -11599,6 +11599,11 @@ SELECT * FROM result_tbl ORDER BY a;
 (3 rows)
 
 DELETE FROM result_tbl;
+-- Test COPY TO when foreign table is partition
+COPY async_pt TO stdout; --error
+ERROR:  cannot copy from foreign table "async_p1"
+DETAIL:  Partition "async_p1" is a foreign table in partitioned table "async_pt"
+HINT:  Try the COPY (SELECT ...) TO variant.
 DROP FOREIGN TABLE async_p3;
 DROP TABLE base_tbl3;
 -- Check case where the partitioned table has local/remote partitions

contrib/postgres_fdw/sql/postgres_fdw.sql

@@ -3941,6 +3941,9 @@ INSERT INTO result_tbl SELECT * FROM async_pt WHERE b === 505;
 SELECT * FROM result_tbl ORDER BY a;
 DELETE FROM result_tbl;
 
+-- Test COPY TO when foreign table is partition
+COPY async_pt TO stdout; --error
+
 DROP FOREIGN TABLE async_p3;
 DROP TABLE base_tbl3;
 

doc/src/sgml/ref/copy.sgml

@@ -539,13 +539,14 @@ COPY <replaceable class="parameter">count</replaceable>
 
    <para>
     <command>COPY TO</command> can be used with plain
-    tables and populated materialized views.
-    For example,
-    <literal>COPY <replaceable class="parameter">table</replaceable>
-    TO</literal> copies the same rows as
+    tables, populated materialized views, and partitioned tables.
+    For non-partitioned tables, COPY <replaceable class="parameter">table</replaceable>
+    copies the same rows as
     <literal>SELECT * FROM ONLY <replaceable class="parameter">table</replaceable></literal>.
+    For partitioned tables, it copies the same rows as
+    <literal>SELECT * FROM <replaceable class="parameter">table</replaceable></literal>.
     However it doesn't directly support other relation types,
-    such as partitioned tables, inheritance child tables, or views.
+    such as inheritance child tables, or views.
     To copy all rows from such relations, use <literal>COPY (SELECT * FROM
     <replaceable class="parameter">table</replaceable>) TO</literal>.
    </para>

src/backend/commands/copy.c

@@ -251,11 +251,15 @@ DoCopy(ParseState *pstate, const CopyStmt *stmt,
 			 * relation which we have opened and locked.  Use "ONLY" so that
 			 * COPY retrieves rows from only the target table not any
 			 * inheritance children, the same as when RLS doesn't apply.
+			 *
+			 * However, when copying data from a partitioned table, we don't
+			 * use "ONLY", since we need to retrieve rows from its descendant
+			 * tables too.
 			 */
 			from = makeRangeVar(get_namespace_name(RelationGetNamespace(rel)),
 								pstrdup(RelationGetRelationName(rel)),
 								-1);
-			from->inh = false;	/* apply ONLY */
+			from->inh = (rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE);
 
 			/* Build query */
 			select = makeNode(SelectStmt);

src/backend/commands/copyto.c

@@ -18,7 +18,9 @@
 #include <unistd.h>
 #include <sys/stat.h>
 
+#include "access/table.h"
 #include "access/tableam.h"
+#include "catalog/pg_inherits.h"
 #include "commands/copyapi.h"
 #include "commands/progress.h"
 #include "executor/execdesc.h"
@@ -86,6 +88,7 @@ typedef struct CopyToStateData
 
 	CopyFormatOptions opts;
 	Node	   *whereClause;	/* WHERE condition (or NULL) */
+	List	   *partitions;		/* OID list of partitions to copy data from */
 
 	/*
 	 * Working state
@@ -116,6 +119,8 @@ static void CopyOneRowTo(CopyToState cstate, TupleTableSlot *slot);
 static void CopyAttributeOutText(CopyToState cstate, const char *string);
 static void CopyAttributeOutCSV(CopyToState cstate, const char *string,
 								bool use_quote);
+static void CopyRelationTo(CopyToState cstate, Relation rel, Relation root_rel,
+						   uint64 *processed);
 
 /* built-in format-specific routines */
 static void CopyToTextLikeStart(CopyToState cstate, TupleDesc tupDesc);
@@ -602,6 +607,10 @@ EndCopy(CopyToState cstate)
 	pgstat_progress_end_command();
 
 	MemoryContextDelete(cstate->copycontext);
+
+	if (cstate->partitions)
+		list_free(cstate->partitions);
+
 	pfree(cstate);
 }
 
@@ -643,6 +652,7 @@ BeginCopyTo(ParseState *pstate,
 		PROGRESS_COPY_COMMAND_TO,
 		0
 	};
+	List	   *children = NIL;
 
 	if (rel != NULL && rel->rd_rel->relkind != RELKIND_RELATION)
 	{
@@ -673,11 +683,34 @@ BeginCopyTo(ParseState *pstate,
 					 errmsg("cannot copy from sequence \"%s\"",
 							RelationGetRelationName(rel))));
 		else if (rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
+		{
+			/*
+			 * Collect OIDs of relation containing data, so that later
+			 * DoCopyTo can copy the data from them.
+			 */
+			children = find_all_inheritors(RelationGetRelid(rel), AccessShareLock, NULL);
+
+			foreach_oid(child, children)
+			{
+				char		relkind = get_rel_relkind(child);
+
+				if (relkind == RELKIND_FOREIGN_TABLE)
+				{
+					char	   *relation_name = get_rel_name(child);
+
 					ereport(ERROR,
-					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-					 errmsg("cannot copy from partitioned table \"%s\"",
-							RelationGetRelationName(rel)),
-					 errhint("Try the COPY (SELECT ...) TO variant.")));
+							errcode(ERRCODE_WRONG_OBJECT_TYPE),
+							errmsg("cannot copy from foreign table \"%s\"", relation_name),
+							errdetail("Partition \"%s\" is a foreign table in partitioned table \"%s\"",
+									  relation_name, RelationGetRelationName(rel)),
+							errhint("Try the COPY (SELECT ...) TO variant."));
+				}
+
+				/* Exclude tables with no data */
+				if (RELKIND_HAS_PARTITIONS(relkind))
+					children = foreach_delete_current(children, child);
+			}
+		}
 		else
 			ereport(ERROR,
 					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
@@ -713,6 +746,7 @@ BeginCopyTo(ParseState *pstate,
 		cstate->rel = rel;
 
 		tupDesc = RelationGetDescr(cstate->rel);
+		cstate->partitions = children;
 	}
 	else
 	{
@@ -722,6 +756,7 @@ BeginCopyTo(ParseState *pstate,
 		DestReceiver *dest;
 
 		cstate->rel = NULL;
+		cstate->partitions = NIL;
 
 		/*
 		 * Run parse analysis and rewrite.  Note this also acquires sufficient
@@ -1030,7 +1065,7 @@ DoCopyTo(CopyToState cstate)
 	TupleDesc	tupDesc;
 	int			num_phys_attrs;
 	ListCell   *cur;
-	uint64		processed;
+	uint64		processed = 0;
 
 	if (fe_copy)
 		SendCopyBegin(cstate);
@@ -1069,50 +1104,108 @@ DoCopyTo(CopyToState cstate)
 	cstate->routine->CopyToStart(cstate, tupDesc);
 
 	if (cstate->rel)
+	{
+		/*
+		 * If COPY TO source table is a partitioned table, then open each
+		 * partition and process each individual partition.
+		 */
+		if (cstate->rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
+		{
+			foreach_oid(child, cstate->partitions)
+			{
+				Relation	scan_rel;
+
+				/* We already got the lock in BeginCopyTo */
+				scan_rel = table_open(child, NoLock);
+				CopyRelationTo(cstate, scan_rel, cstate->rel, &processed);
+				table_close(scan_rel, NoLock);
+			}
+		}
+		else
+			CopyRelationTo(cstate, cstate->rel, NULL, &processed);
+	}
+	else
+	{
+		/* run the plan --- the dest receiver will send tuples */
+		ExecutorRun(cstate->queryDesc, ForwardScanDirection, 0);
+		processed = ((DR_copy *) cstate->queryDesc->dest)->processed;
+	}
+
+	cstate->routine->CopyToEnd(cstate);
+
+	MemoryContextDelete(cstate->rowcontext);
+
+	if (fe_copy)
+		SendCopyEnd(cstate);
+
+	return processed;
+}
+
+/*
+ * Scans a single table and exports its rows to the COPY destination.
+ *
+ * root_rel can be set to the root table of rel if rel is a partition
+ * table so that we can send tuples in root_rel's rowtype, which might
+ * differ from individual partitions.
+*/
+static void
+CopyRelationTo(CopyToState cstate, Relation rel, Relation root_rel, uint64 *processed)
 {
 	TupleTableSlot *slot;
 	TableScanDesc scandesc;
+	AttrMap    *map = NULL;
+	TupleTableSlot *root_slot = NULL;
 
-		scandesc = table_beginscan(cstate->rel, GetActiveSnapshot(), 0, NULL);
-		slot = table_slot_create(cstate->rel, NULL);
+	scandesc = table_beginscan(rel, GetActiveSnapshot(), 0, NULL);
+	slot = table_slot_create(rel, NULL);
+
+	/*
+	 * If we are exporting partition data here, we check if converting tuples
+	 * to the root table's rowtype, because a partition might have column
+	 * order different than its root table.
+	 */
+	if (root_rel != NULL)
+	{
+		root_slot = table_slot_create(root_rel, NULL);
+		map = build_attrmap_by_name_if_req(RelationGetDescr(root_rel),
+										   RelationGetDescr(rel),
+										   false);
+	}
 
-		processed = 0;
 	while (table_scan_getnextslot(scandesc, ForwardScanDirection, slot))
 	{
+		TupleTableSlot *copyslot;
+
 		CHECK_FOR_INTERRUPTS();
 
-			/* Deconstruct the tuple ... */
+		if (map != NULL)
+			copyslot = execute_attr_map_slot(map, slot, root_slot);
+		else
+		{
+			/* Deconstruct the tuple */
 			slot_getallattrs(slot);
+			copyslot = slot;
+		}
 
 		/* Format and send the data */
-			CopyOneRowTo(cstate, slot);
+		CopyOneRowTo(cstate, copyslot);
 
 		/*
-			 * Increment the number of processed tuples, and report the
-			 * progress.
+		 * Increment the number of processed tuples, and report the progress.
 		 */
 		pgstat_progress_update_param(PROGRESS_COPY_TUPLES_PROCESSED,
-										 ++processed);
+									 ++(*processed));
 	}
 
 	ExecDropSingleTupleTableSlot(slot);
-		table_endscan(scandesc);
-	}
-	else
-	{
-		/* run the plan --- the dest receiver will send tuples */
-		ExecutorRun(cstate->queryDesc, ForwardScanDirection, 0);
-		processed = ((DR_copy *) cstate->queryDesc->dest)->processed;
-	}
 
-	cstate->routine->CopyToEnd(cstate);
+	if (root_slot != NULL)
+		ExecDropSingleTupleTableSlot(root_slot);
 
-	MemoryContextDelete(cstate->rowcontext);
+	if (map != NULL)
+		free_attrmap(map);
 
-	if (fe_copy)
-		SendCopyEnd(cstate);
-
-	return processed;
+	table_endscan(scandesc);
 }
 
 /*

src/test/regress/expected/copy.out

@@ -373,3 +373,23 @@ COPY copytest_mv(id) TO stdout WITH (header);
 id
 1
 DROP MATERIALIZED VIEW copytest_mv;
+-- Tests for COPY TO with partitioned tables.
+-- The child table pp_2 has a different column order than the root table pp.
+-- Check if COPY TO exports tuples as the root table's column order.
+CREATE TABLE pp (id int,val int) PARTITION BY RANGE (id);
+CREATE TABLE pp_1 (val int, id int) PARTITION BY RANGE (id);
+CREATE TABLE pp_2 (id int, val int) PARTITION BY RANGE (id);
+ALTER TABLE pp ATTACH PARTITION pp_1 FOR VALUES FROM (1) TO (5);
+ALTER TABLE pp ATTACH PARTITION pp_2 FOR VALUES FROM (5) TO (10);
+CREATE TABLE pp_15 PARTITION OF pp_1 FOR VALUES FROM (1) TO (5);
+CREATE TABLE pp_510 PARTITION OF pp_2 FOR VALUES FROM (5) TO (10);
+INSERT INTO pp SELECT g, 10 + g FROM generate_series(1,6) g;
+COPY pp TO stdout(header);
+id	val
+1	11
+2	12
+3	13
+4	14
+5	15
+6	16
+DROP TABLE PP;

src/test/regress/expected/rowsecurity.out

@@ -986,6 +986,11 @@ NOTICE:  f_leak => my first satire
    9 |  11 |      1 | regress_rls_dave  | awesome science fiction
 (4 rows)
 
+COPY part_document TO stdout WITH (DELIMITER ',');
+1,11,1,regress_rls_bob,my first novel
+6,11,1,regress_rls_carol,great science fiction
+9,11,1,regress_rls_dave,awesome science fiction
+4,55,1,regress_rls_bob,my first satire
 EXPLAIN (COSTS OFF) SELECT * FROM part_document WHERE f_leak(dtitle);
                                QUERY PLAN                                
 -------------------------------------------------------------------------
@@ -1028,6 +1033,17 @@ NOTICE:  f_leak => awesome technology book
   10 |  99 |      2 | regress_rls_dave  | awesome technology book
 (10 rows)
 
+COPY part_document TO stdout WITH (DELIMITER ',');
+1,11,1,regress_rls_bob,my first novel
+2,11,2,regress_rls_bob,my second novel
+6,11,1,regress_rls_carol,great science fiction
+9,11,1,regress_rls_dave,awesome science fiction
+4,55,1,regress_rls_bob,my first satire
+8,55,2,regress_rls_carol,great satire
+3,99,2,regress_rls_bob,my science textbook
+5,99,2,regress_rls_bob,my history book
+7,99,2,regress_rls_carol,great technology book
+10,99,2,regress_rls_dave,awesome technology book
 EXPLAIN (COSTS OFF) SELECT * FROM part_document WHERE f_leak(dtitle);
                                QUERY PLAN                                
 -------------------------------------------------------------------------
@@ -1058,6 +1074,11 @@ NOTICE:  f_leak => awesome science fiction
    9 |  11 |      1 | regress_rls_dave  | awesome science fiction
 (4 rows)
 
+COPY part_document TO stdout WITH (DELIMITER ',');
+1,11,1,regress_rls_bob,my first novel
+2,11,2,regress_rls_bob,my second novel
+6,11,1,regress_rls_carol,great science fiction
+9,11,1,regress_rls_dave,awesome science fiction
 EXPLAIN (COSTS OFF) SELECT * FROM part_document WHERE f_leak(dtitle);
                                     QUERY PLAN                                    
 ----------------------------------------------------------------------------------

src/test/regress/sql/copy.sql

@@ -405,3 +405,17 @@ COPY copytest_mv(id) TO stdout WITH (header);
 REFRESH MATERIALIZED VIEW copytest_mv;
 COPY copytest_mv(id) TO stdout WITH (header);
 DROP MATERIALIZED VIEW copytest_mv;
+
+-- Tests for COPY TO with partitioned tables.
+-- The child table pp_2 has a different column order than the root table pp.
+-- Check if COPY TO exports tuples as the root table's column order.
+CREATE TABLE pp (id int,val int) PARTITION BY RANGE (id);
+CREATE TABLE pp_1 (val int, id int) PARTITION BY RANGE (id);
+CREATE TABLE pp_2 (id int, val int) PARTITION BY RANGE (id);
+ALTER TABLE pp ATTACH PARTITION pp_1 FOR VALUES FROM (1) TO (5);
+ALTER TABLE pp ATTACH PARTITION pp_2 FOR VALUES FROM (5) TO (10);
+CREATE TABLE pp_15 PARTITION OF pp_1 FOR VALUES FROM (1) TO (5);
+CREATE TABLE pp_510 PARTITION OF pp_2 FOR VALUES FROM (5) TO (10);
+INSERT INTO pp SELECT g, 10 + g FROM generate_series(1,6) g;
+COPY pp TO stdout(header);
+DROP TABLE PP;

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