Properly set relpersistence for fake relcache entries.

This can result in buffers failing to be properly flushed at
checkpoint time, leading to data loss.

Report, diagnosis, and patch by Jeff Davis.

src/backend/access/transam/xlogutils.c

@@ -394,6 +394,8 @@ CreateFakeRelcacheEntry(RelFileNode rnode)
 	FakeRelCacheEntry fakeentry;
 	Relation	rel;
 
+	Assert(InRecovery);
+
 	/* Allocate the Relation struct and all related space in one block. */
 	fakeentry = palloc0(sizeof(FakeRelCacheEntryData));
 	rel = (Relation) fakeentry;
@@ -403,6 +405,9 @@ CreateFakeRelcacheEntry(RelFileNode rnode)
 	/* We will never be working with temp rels during recovery */
 	rel->rd_backend = InvalidBackendId;
 
+	/* It must be a permanent table if we're in recovery. */
+	rel->rd_rel->relpersistence = RELPERSISTENCE_PERMANENT;
+
 	/* We don't know the name of the relation; use relfilenode instead */
 	sprintf(RelationGetRelationName(rel), "%u", rnode.relNode);
 

src/backend/storage/buffer/bufmgr.c

@@ -271,6 +271,8 @@ ReadBufferWithoutRelcache(RelFileNode rnode, ForkNumber forkNum,
 
 	SMgrRelation smgr = smgropen(rnode, InvalidBackendId);
 
+	Assert(InRecovery);
+
 	return ReadBuffer_common(smgr, RELPERSISTENCE_PERMANENT, forkNum, blockNum,
 							 mode, strategy, &hit);
 }