Backport addition of rs_old_rel to rewriteheap's state.

Originally part of b89e151, the
introduction of logical decoding, this is required to backport a
commit introducing error checks defending against recent bugs.

It's possible that extensions calls begin_heap_rewrite(), but it seems
highly unlikely. But if so, they'd break.

Author: Andres Freund
Discussion: https://postgr.es/m/20171215010029.3dxx56vjlymudvwo@alap3.anarazel.de

Author: anarazel

src/backend/access/heap/rewriteheap.c

@@ -120,6 +120,7 @@
  */
 typedef struct RewriteStateData
 {
+	Relation	rs_old_rel;		/* source heap */
 	Relation	rs_new_rel;		/* destination heap */
 	Page		rs_buffer;		/* page currently being built */
 	BlockNumber rs_blockno;		/* block where page will go */
@@ -187,7 +188,7 @@ static void raw_heap_insert(RewriteState state, HeapTuple tup);
  * to be used in subsequent calls to the other functions.
  */
 RewriteState
-begin_heap_rewrite(Relation new_heap, TransactionId oldest_xmin,
+begin_heap_rewrite(Relation old_heap, Relation new_heap, TransactionId oldest_xmin,
 				   TransactionId freeze_xid, MultiXactId cutoff_multi,
 				   bool use_wal)
 {
@@ -210,6 +211,7 @@ begin_heap_rewrite(Relation new_heap, TransactionId oldest_xmin,
 	/* Create and fill in the state struct */
 	state = palloc0(sizeof(RewriteStateData));
 
+	state->rs_old_rel = old_heap;
 	state->rs_new_rel = new_heap;
 	state->rs_buffer = (Page) palloc(BLCKSZ);
 	/* new_heap needn't be empty, just locked */

src/backend/commands/cluster.c

@@ -887,7 +887,7 @@ copy_heap_data(Oid OIDNewHeap, Oid OIDOldHeap, Oid OIDOldIndex,
 	is_system_catalog = IsSystemRelation(OldHeap);
 
 	/* Initialize the rewrite operation */
-	rwstate = begin_heap_rewrite(NewHeap, OldestXmin, FreezeXid,
+	rwstate = begin_heap_rewrite(OldHeap, NewHeap, OldestXmin, FreezeXid,
 								 MultiXactCutoff, use_wal);
 
 	/*

src/include/access/rewriteheap.h

@@ -19,7 +19,7 @@
 /* struct definition is private to rewriteheap.c */
 typedef struct RewriteStateData *RewriteState;
 
-extern RewriteState begin_heap_rewrite(Relation NewHeap,
+extern RewriteState begin_heap_rewrite(Relation OldHeap, Relation NewHeap,
 				   TransactionId OldestXmin, TransactionId FreezeXid,
 				   MultiXactId MultiXactCutoff, bool use_wal);
 extern void end_heap_rewrite(RewriteState state);