logical decoding: old/newtuple in spooled UPDATE changes was switched around.

Somehow I managed to flip the order of restoring old & new tuples when
de-spooling a change in a large transaction from disk. This happens to
only take effect when a change is spooled to disk which has old/new
versions of the tuple. That only is the case for UPDATEs where he
primary key changed or where replica identity is changed to FULL.

The tests didn't catch this because either spooled updates, or updates
that changed primary keys, were tested; not both at the same time.

Found while adding tests for the following commit.

Backpatch: 9.4, where logical decoding was added

3 files changed, 37 insertions, 10 deletions

diff --git a/contrib/test_decoding/expected/ddl.out b/contrib/test_decoding/expected/ddl.out
index a48d42c5a14..f0498aa302c 100644
--- a/contrib/test_decoding/expected/ddl.out
+++ b/contrib/test_decoding/expected/ddl.out
@@ -240,6 +240,21 @@ ORDER BY 1,2;
  20467 | table public.tr_etoomuch: DELETE: id[integer]:1 | table public.tr_etoomuch: UPDATE: id[integer]:9999 data[integer]:-9999
 (3 rows)
 
+-- check updates of primary keys work correctly
+BEGIN;
+CREATE TABLE spoolme AS SELECT g.i FROM generate_series(1, 5000) g(i);
+UPDATE tr_etoomuch SET id = -id WHERE id = 5000;
+DELETE FROM spoolme;
+DROP TABLE spoolme;
+COMMIT;
+SELECT data
+FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1')
+WHERE data ~ 'UPDATE';
+                                                    data                                                     
+-------------------------------------------------------------------------------------------------------------
+ table public.tr_etoomuch: UPDATE: old-key: id[integer]:5000 new-tuple: id[integer]:-5000 data[integer]:5000
+(1 row)
+
 -- check that a large, spooled, upsert works
 INSERT INTO tr_etoomuch (id, data)
 SELECT g.i, -g.i FROM generate_series(8000, 12000) g(i)
diff --git a/contrib/test_decoding/sql/ddl.sql b/contrib/test_decoding/sql/ddl.sql
index e311c5966e0..ad928ad5726 100644
--- a/contrib/test_decoding/sql/ddl.sql
+++ b/contrib/test_decoding/sql/ddl.sql
@@ -123,6 +123,18 @@ FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids',
 GROUP BY substring(data, 1, 24)
 ORDER BY 1,2;
 
+-- check updates of primary keys work correctly
+BEGIN;
+CREATE TABLE spoolme AS SELECT g.i FROM generate_series(1, 5000) g(i);
+UPDATE tr_etoomuch SET id = -id WHERE id = 5000;
+DELETE FROM spoolme;
+DROP TABLE spoolme;
+COMMIT;
+
+SELECT data
+FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1')
+WHERE data ~ 'UPDATE';
+
 -- check that a large, spooled, upsert works
 INSERT INTO tr_etoomuch (id, data)
 SELECT g.i, -g.i FROM generate_series(8000, 12000) g(i)
diff --git a/src/backend/replication/logical/reorderbuffer.c b/src/backend/replication/logical/reorderbuffer.c
index b3276c74c7c..2f4489d1b3e 100644
--- a/src/backend/replication/logical/reorderbuffer.c
+++ b/src/backend/replication/logical/reorderbuffer.c
@@ -2335,27 +2335,27 @@ ReorderBufferRestoreChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
 		case REORDER_BUFFER_CHANGE_UPDATE:
 		case REORDER_BUFFER_CHANGE_DELETE:
 		case REORDER_BUFFER_CHANGE_INTERNAL_SPEC_INSERT:
-			if (change->data.tp.newtuple)
+			if (change->data.tp.oldtuple)
 			{
 				Size		len = offsetof(ReorderBufferTupleBuf, t_data) +
 				((ReorderBufferTupleBuf *) data)->tuple.t_len;
 
-				change->data.tp.newtuple = ReorderBufferGetTupleBuf(rb);
-				memcpy(change->data.tp.newtuple, data, len);
-				change->data.tp.newtuple->tuple.t_data =
-					&change->data.tp.newtuple->t_data.header;
+				change->data.tp.oldtuple = ReorderBufferGetTupleBuf(rb);
+				memcpy(change->data.tp.oldtuple, data, len);
+				change->data.tp.oldtuple->tuple.t_data =
+					&change->data.tp.oldtuple->t_data.header;
 				data += len;
 			}
 
-			if (change->data.tp.oldtuple)
+			if (change->data.tp.newtuple)
 			{
 				Size		len = offsetof(ReorderBufferTupleBuf, t_data) +
 				((ReorderBufferTupleBuf *) data)->tuple.t_len;
 
-				change->data.tp.oldtuple = ReorderBufferGetTupleBuf(rb);
-				memcpy(change->data.tp.oldtuple, data, len);
-				change->data.tp.oldtuple->tuple.t_data =
-					&change->data.tp.oldtuple->t_data.header;
+				change->data.tp.newtuple = ReorderBufferGetTupleBuf(rb);
+				memcpy(change->data.tp.newtuple, data, len);
+				change->data.tp.newtuple->tuple.t_data =
+					&change->data.tp.newtuple->t_data.header;
 				data += len;
 			}
 			break;