Remove unportable use of anonymous unions from reorderbuffer.h.

In b89e1510 I had assumed it was ok to use anonymous unions as
struct members, but while a longstanding extension in many compilers,
it's only been standardized in C11.

To fix, remove one of the anonymous unions which tried to hide some
implementation specific enum values and give the other a name. The
latter unfortunately requires changes in output plugins, but since the
feature has only been added a few days ago...

Andres Freund

contrib/test_decoding/test_decoding.c

@@ -358,43 +358,45 @@ pg_decode_change(LogicalDecodingContext *ctx, ReorderBufferTXN *txn,
 	{
 		case REORDER_BUFFER_CHANGE_INSERT:
 			appendStringInfoString(ctx->out, " INSERT:");
-			if (change->tp.newtuple == NULL)
+			if (change->data.tp.newtuple == NULL)
 				appendStringInfoString(ctx->out, " (no-tuple-data)");
 			else
 				tuple_to_stringinfo(ctx->out, tupdesc,
-									&change->tp.newtuple->tuple,
+									&change->data.tp.newtuple->tuple,
 									false);
 			break;
 		case REORDER_BUFFER_CHANGE_UPDATE:
 			appendStringInfoString(ctx->out, " UPDATE:");
-			if (change->tp.oldtuple != NULL)
+			if (change->data.tp.oldtuple != NULL)
 			{
 				appendStringInfoString(ctx->out, " old-key:");
 				tuple_to_stringinfo(ctx->out, tupdesc,
-									&change->tp.oldtuple->tuple,
+									&change->data.tp.oldtuple->tuple,
 									true);
 				appendStringInfoString(ctx->out, " new-tuple:");
 			}
 
-			if (change->tp.newtuple == NULL)
+			if (change->data.tp.newtuple == NULL)
 				appendStringInfoString(ctx->out, " (no-tuple-data)");
 			else
 				tuple_to_stringinfo(ctx->out, tupdesc,
-									&change->tp.newtuple->tuple,
+									&change->data.tp.newtuple->tuple,
 									false);
 			break;
 		case REORDER_BUFFER_CHANGE_DELETE:
 			appendStringInfoString(ctx->out, " DELETE:");
 
 			/* if there was no PK, we only know that a delete happened */
-			if (change->tp.oldtuple == NULL)
+			if (change->data.tp.oldtuple == NULL)
 				appendStringInfoString(ctx->out, " (no-tuple-data)");
 			/* In DELETE, only the replica identity is present; display that */
 			else
 				tuple_to_stringinfo(ctx->out, tupdesc,
-									&change->tp.oldtuple->tuple,
+									&change->data.tp.oldtuple->tuple,
 									true);
 			break;
+		default:
+			Assert(false);
 	}
 
 	MemoryContextSwitchTo(old);

src/backend/replication/logical/decode.c

@@ -586,17 +586,17 @@ DecodeInsert(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 
 	change = ReorderBufferGetChange(ctx->reorder);
 	change->action = REORDER_BUFFER_CHANGE_INSERT;
-	memcpy(&change->tp.relnode, &xlrec->target.node, sizeof(RelFileNode));
+	memcpy(&change->data.tp.relnode, &xlrec->target.node, sizeof(RelFileNode));
 
 	if (xlrec->flags & XLOG_HEAP_CONTAINS_NEW_TUPLE)
 	{
 		Assert(r->xl_len > (SizeOfHeapInsert + SizeOfHeapHeader));
 
-		change->tp.newtuple = ReorderBufferGetTupleBuf(ctx->reorder);
+		change->data.tp.newtuple = ReorderBufferGetTupleBuf(ctx->reorder);
 
 		DecodeXLogTuple((char *) xlrec + SizeOfHeapInsert,
 						r->xl_len - SizeOfHeapInsert,
-						change->tp.newtuple);
+						change->data.tp.newtuple);
 	}
 
 	ReorderBufferQueueChange(ctx->reorder, r->xl_xid, buf->origptr, change);
@@ -626,7 +626,7 @@ DecodeUpdate(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 
 	change = ReorderBufferGetChange(ctx->reorder);
 	change->action = REORDER_BUFFER_CHANGE_UPDATE;
-	memcpy(&change->tp.relnode, &xlrec->target.node, sizeof(RelFileNode));
+	memcpy(&change->data.tp.relnode, &xlrec->target.node, sizeof(RelFileNode));
 
 	data = (char *) &xlhdr->header;
 
@@ -634,11 +634,11 @@ DecodeUpdate(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 	{
 		Assert(r->xl_len > (SizeOfHeapUpdate + SizeOfHeapHeaderLen));
 
-		change->tp.newtuple = ReorderBufferGetTupleBuf(ctx->reorder);
+		change->data.tp.newtuple = ReorderBufferGetTupleBuf(ctx->reorder);
 
 		DecodeXLogTuple(data,
 						xlhdr->t_len + SizeOfHeapHeader,
-						change->tp.newtuple);
+						change->data.tp.newtuple);
 		/* skip over the rest of the tuple header */
 		data += SizeOfHeapHeader;
 		/* skip over the tuple data */
@@ -648,10 +648,10 @@ DecodeUpdate(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 	if (xlrec->flags & XLOG_HEAP_CONTAINS_OLD)
 	{
 		xlhdr = (xl_heap_header_len *) data;
-		change->tp.oldtuple = ReorderBufferGetTupleBuf(ctx->reorder);
+		change->data.tp.oldtuple = ReorderBufferGetTupleBuf(ctx->reorder);
 		DecodeXLogTuple((char *) &xlhdr->header,
 						xlhdr->t_len + SizeOfHeapHeader,
-						change->tp.oldtuple);
+						change->data.tp.oldtuple);
 		data = (char *) &xlhdr->header;
 		data += SizeOfHeapHeader;
 		data += xlhdr->t_len;
@@ -681,18 +681,18 @@ DecodeDelete(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 	change = ReorderBufferGetChange(ctx->reorder);
 	change->action = REORDER_BUFFER_CHANGE_DELETE;
 
-	memcpy(&change->tp.relnode, &xlrec->target.node, sizeof(RelFileNode));
+	memcpy(&change->data.tp.relnode, &xlrec->target.node, sizeof(RelFileNode));
 
 	/* old primary key stored */
 	if (xlrec->flags & XLOG_HEAP_CONTAINS_OLD)
 	{
 		Assert(r->xl_len > (SizeOfHeapDelete + SizeOfHeapHeader));
 
-		change->tp.oldtuple = ReorderBufferGetTupleBuf(ctx->reorder);
+		change->data.tp.oldtuple = ReorderBufferGetTupleBuf(ctx->reorder);
 
 		DecodeXLogTuple((char *) xlrec + SizeOfHeapDelete,
 						r->xl_len - SizeOfHeapDelete,
-						change->tp.oldtuple);
+						change->data.tp.oldtuple);
 	}
 	ReorderBufferQueueChange(ctx->reorder, r->xl_xid, buf->origptr, change);
 }
@@ -735,7 +735,7 @@ DecodeMultiInsert(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 
 		change = ReorderBufferGetChange(ctx->reorder);
 		change->action = REORDER_BUFFER_CHANGE_INSERT;
-		memcpy(&change->tp.relnode, &xlrec->node, sizeof(RelFileNode));
+		memcpy(&change->data.tp.relnode, &xlrec->node, sizeof(RelFileNode));
 
 		/*
 		 * CONTAINS_NEW_TUPLE will always be set currently as multi_insert
@@ -746,9 +746,9 @@ DecodeMultiInsert(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 		 */
 		if (xlrec->flags & XLOG_HEAP_CONTAINS_NEW_TUPLE)
 		{
-			change->tp.newtuple = ReorderBufferGetTupleBuf(ctx->reorder);
+			change->data.tp.newtuple = ReorderBufferGetTupleBuf(ctx->reorder);
 
-			tuple = change->tp.newtuple;
+			tuple = change->data.tp.newtuple;
 
 			/* not a disk based tuple */
 			ItemPointerSetInvalid(&tuple->tuple.t_self);

src/backend/replication/logical/reorderbuffer.c

@@ -80,26 +80,6 @@
 #include "utils/relfilenodemap.h"
 #include "utils/tqual.h"
 
-/*
- * For efficiency and simplicity reasons we want to keep Snapshots, CommandIds
- * and ComboCids in the same list with the user visible INSERT/UPDATE/DELETE
- * changes. We don't want to leak those internal values to external users
- * though (they would just use switch()...default:) because that would make it
- * harder to add to new user visible values.
- *
- * This needs to be synchronized with ReorderBufferChangeType! Adjust the
- * StaticAssertExpr's in ReorderBufferAllocate if you add anything!
- */
-typedef enum
-{
-	REORDER_BUFFER_CHANGE_INTERNAL_INSERT,
-	REORDER_BUFFER_CHANGE_INTERNAL_UPDATE,
-	REORDER_BUFFER_CHANGE_INTERNAL_DELETE,
-	REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT,
-	REORDER_BUFFER_CHANGE_INTERNAL_COMMAND_ID,
-	REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID
-} ReorderBufferChangeTypeInternal;
-
 /* entry for a hash table we use to map from xid to our transaction state */
 typedef struct ReorderBufferTXNByIdEnt
 {
@@ -255,10 +235,6 @@ ReorderBufferAllocate(void)
 	HASHCTL		hash_ctl;
 	MemoryContext new_ctx;
 
-	StaticAssertExpr((int) REORDER_BUFFER_CHANGE_INTERNAL_INSERT == (int) REORDER_BUFFER_CHANGE_INSERT, "out of sync enums");
-	StaticAssertExpr((int) REORDER_BUFFER_CHANGE_INTERNAL_UPDATE == (int) REORDER_BUFFER_CHANGE_UPDATE, "out of sync enums");
-	StaticAssertExpr((int) REORDER_BUFFER_CHANGE_INTERNAL_DELETE == (int) REORDER_BUFFER_CHANGE_DELETE, "out of sync enums");
-
 	/* allocate memory in own context, to have better accountability */
 	new_ctx = AllocSetContextCreate(CurrentMemoryContext,
 									"ReorderBuffer",
@@ -427,28 +403,28 @@ void
 ReorderBufferReturnChange(ReorderBuffer *rb, ReorderBufferChange *change)
 {
 	/* free contained data */
-	switch ((ReorderBufferChangeTypeInternal) change->action_internal)
+	switch (change->action)
 	{
-		case REORDER_BUFFER_CHANGE_INTERNAL_INSERT:
-		case REORDER_BUFFER_CHANGE_INTERNAL_UPDATE:
-		case REORDER_BUFFER_CHANGE_INTERNAL_DELETE:
-			if (change->tp.newtuple)
+		case REORDER_BUFFER_CHANGE_INSERT:
+		case REORDER_BUFFER_CHANGE_UPDATE:
+		case REORDER_BUFFER_CHANGE_DELETE:
+			if (change->data.tp.newtuple)
 			{
-				ReorderBufferReturnTupleBuf(rb, change->tp.newtuple);
-				change->tp.newtuple = NULL;
+				ReorderBufferReturnTupleBuf(rb, change->data.tp.newtuple);
+				change->data.tp.newtuple = NULL;
 			}
 
-			if (change->tp.oldtuple)
+			if (change->data.tp.oldtuple)
 			{
-				ReorderBufferReturnTupleBuf(rb, change->tp.oldtuple);
-				change->tp.oldtuple = NULL;
+				ReorderBufferReturnTupleBuf(rb, change->data.tp.oldtuple);
+				change->data.tp.oldtuple = NULL;
 			}
 			break;
 		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
-			if (change->snapshot)
+			if (change->data.snapshot)
 			{
-				ReorderBufferFreeSnap(rb, change->snapshot);
-				change->snapshot = NULL;
+				ReorderBufferFreeSnap(rb, change->data.snapshot);
+				change->data.snapshot = NULL;
 			}
 			break;
 		case REORDER_BUFFER_CHANGE_INTERNAL_COMMAND_ID:
@@ -1086,7 +1062,7 @@ ReorderBufferCleanupTXN(ReorderBuffer *rb, ReorderBufferTXN *txn)
 		ReorderBufferChange *change;
 
 		change = dlist_container(ReorderBufferChange, node, iter.cur);
-		Assert(change->action_internal == REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID);
+		Assert(change->action == REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID);
 		ReorderBufferReturnChange(rb, change);
 	}
 
@@ -1161,14 +1137,14 @@ ReorderBufferBuildTupleCidHash(ReorderBuffer *rb, ReorderBufferTXN *txn)
 
 		change = dlist_container(ReorderBufferChange, node, iter.cur);
 
-		Assert(change->action_internal == REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID);
+		Assert(change->action == REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID);
 
 		/* be careful about padding */
 		memset(&key, 0, sizeof(ReorderBufferTupleCidKey));
 
-		key.relnode = change->tuplecid.node;
+		key.relnode = change->data.tuplecid.node;
 
-		ItemPointerCopy(&change->tuplecid.tid,
+		ItemPointerCopy(&change->data.tuplecid.tid,
 						&key.tid);
 
 		ent = (ReorderBufferTupleCidEnt *)
@@ -1178,22 +1154,22 @@ ReorderBufferBuildTupleCidHash(ReorderBuffer *rb, ReorderBufferTXN *txn)
 						&found);
 		if (!found)
 		{
-			ent->cmin = change->tuplecid.cmin;
-			ent->cmax = change->tuplecid.cmax;
-			ent->combocid = change->tuplecid.combocid;
+			ent->cmin = change->data.tuplecid.cmin;
+			ent->cmax = change->data.tuplecid.cmax;
+			ent->combocid = change->data.tuplecid.combocid;
 		}
 		else
 		{
-			Assert(ent->cmin == change->tuplecid.cmin);
+			Assert(ent->cmin == change->data.tuplecid.cmin);
 			Assert(ent->cmax == InvalidCommandId ||
-				   ent->cmax == change->tuplecid.cmax);
+				   ent->cmax == change->data.tuplecid.cmax);
 
 			/*
 			 * if the tuple got valid in this transaction and now got deleted
 			 * we already have a valid cmin stored. The cmax will be
 			 * InvalidCommandId though.
 			 */
-			ent->cmax = change->tuplecid.cmax;
+			ent->cmax = change->data.tuplecid.cmax;
 		}
 	}
 }
@@ -1367,33 +1343,33 @@ ReorderBufferCommit(ReorderBuffer *rb, TransactionId xid,
 			Relation	relation = NULL;
 			Oid			reloid;
 
-			switch ((ReorderBufferChangeTypeInternal) change->action_internal)
+			switch (change->action)
 			{
-				case REORDER_BUFFER_CHANGE_INTERNAL_INSERT:
-				case REORDER_BUFFER_CHANGE_INTERNAL_UPDATE:
-				case REORDER_BUFFER_CHANGE_INTERNAL_DELETE:
+				case REORDER_BUFFER_CHANGE_INSERT:
+				case REORDER_BUFFER_CHANGE_UPDATE:
+				case REORDER_BUFFER_CHANGE_DELETE:
 					Assert(snapshot_now);
 
-					reloid = RelidByRelfilenode(change->tp.relnode.spcNode,
-												change->tp.relnode.relNode);
+					reloid = RelidByRelfilenode(change->data.tp.relnode.spcNode,
+												change->data.tp.relnode.relNode);
 
 					/*
 					 * Catalog tuple without data, emitted while catalog was
 					 * in the process of being rewritten.
 					 */
 					if (reloid == InvalidOid &&
-						change->tp.newtuple == NULL &&
-						change->tp.oldtuple == NULL)
+						change->data.tp.newtuple == NULL &&
+						change->data.tp.oldtuple == NULL)
 						continue;
 					else if (reloid == InvalidOid)
 						elog(ERROR, "could not lookup relation %s",
-							 relpathperm(change->tp.relnode, MAIN_FORKNUM));
+							 relpathperm(change->data.tp.relnode, MAIN_FORKNUM));
 
 					relation = RelationIdGetRelation(reloid);
 
 					if (relation == NULL)
 						elog(ERROR, "could open relation descriptor %s",
-							 relpathperm(change->tp.relnode, MAIN_FORKNUM));
+							 relpathperm(change->data.tp.relnode, MAIN_FORKNUM));
 
 					if (RelationIsLogicallyLogged(relation))
 					{
@@ -1440,7 +1416,7 @@ ReorderBufferCommit(ReorderBuffer *rb, TransactionId xid,
 					{
 						ReorderBufferFreeSnap(rb, snapshot_now);
 						snapshot_now =
-							ReorderBufferCopySnap(rb, change->snapshot,
+							ReorderBufferCopySnap(rb, change->data.snapshot,
 												  txn, command_id);
 					}
 					/*
@@ -1448,15 +1424,15 @@ ReorderBufferCommit(ReorderBuffer *rb, TransactionId xid,
 					 * free. We could introduce refcounting for that, but for
 					 * now this seems infrequent enough not to care.
 					 */
-					else if (change->snapshot->copied)
+					else if (change->data.snapshot->copied)
 					{
 						snapshot_now =
-							ReorderBufferCopySnap(rb, change->snapshot,
+							ReorderBufferCopySnap(rb, change->data.snapshot,
 												  txn, command_id);
 					}
 					else
 					{
-						snapshot_now = change->snapshot;
+						snapshot_now = change->data.snapshot;
 					}
 
 
@@ -1465,11 +1441,11 @@ ReorderBufferCommit(ReorderBuffer *rb, TransactionId xid,
 					break;
 
 				case REORDER_BUFFER_CHANGE_INTERNAL_COMMAND_ID:
-					Assert(change->command_id != InvalidCommandId);
+					Assert(change->data.command_id != InvalidCommandId);
 
-					if (command_id < change->command_id)
+					if (command_id < change->data.command_id)
 					{
-						command_id = change->command_id;
+						command_id = change->data.command_id;
 
 						if (!snapshot_now->copied)
 						{
@@ -1712,8 +1688,8 @@ ReorderBufferAddSnapshot(ReorderBuffer *rb, TransactionId xid,
 {
 	ReorderBufferChange *change = ReorderBufferGetChange(rb);
 
-	change->snapshot = snap;
-	change->action_internal = REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT;
+	change->data.snapshot = snap;
+	change->action = REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT;
 
 	ReorderBufferQueueChange(rb, xid, lsn, change);
 }
@@ -1752,8 +1728,8 @@ ReorderBufferAddNewCommandId(ReorderBuffer *rb, TransactionId xid,
 {
 	ReorderBufferChange *change = ReorderBufferGetChange(rb);
 
-	change->command_id = cid;
-	change->action_internal = REORDER_BUFFER_CHANGE_INTERNAL_COMMAND_ID;
+	change->data.command_id = cid;
+	change->action = REORDER_BUFFER_CHANGE_INTERNAL_COMMAND_ID;
 
 	ReorderBufferQueueChange(rb, xid, lsn, change);
 }
@@ -1773,13 +1749,13 @@ ReorderBufferAddNewTupleCids(ReorderBuffer *rb, TransactionId xid,
 
 	txn = ReorderBufferTXNByXid(rb, xid, true, NULL, lsn, true);
 
-	change->tuplecid.node = node;
-	change->tuplecid.tid = tid;
-	change->tuplecid.cmin = cmin;
-	change->tuplecid.cmax = cmax;
-	change->tuplecid.combocid = combocid;
+	change->data.tuplecid.node = node;
+	change->data.tuplecid.tid = tid;
+	change->data.tuplecid.cmin = cmin;
+	change->data.tuplecid.cmax = cmax;
+	change->data.tuplecid.combocid = combocid;
 	change->lsn = lsn;
-	change->action_internal = REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID;
+	change->action = REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID;
 
 	dlist_push_tail(&txn->tuplecids, &change->node);
 	txn->ntuplecids++;
@@ -2017,26 +1993,30 @@ ReorderBufferSerializeChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
 	ondisk = (ReorderBufferDiskChange *) rb->outbuf;
 	memcpy(&ondisk->change, change, sizeof(ReorderBufferChange));
 
-	switch ((ReorderBufferChangeTypeInternal) change->action_internal)
+	switch (change->action)
 	{
-		case REORDER_BUFFER_CHANGE_INTERNAL_INSERT:
+		case REORDER_BUFFER_CHANGE_INSERT:
 			/* fall through */
-		case REORDER_BUFFER_CHANGE_INTERNAL_UPDATE:
+		case REORDER_BUFFER_CHANGE_UPDATE:
 			/* fall through */
-		case REORDER_BUFFER_CHANGE_INTERNAL_DELETE:
+		case REORDER_BUFFER_CHANGE_DELETE:
 			{
 				char	   *data;
+				ReorderBufferTupleBuf *oldtup, *newtup;
 				Size		oldlen = 0;
 				Size		newlen = 0;
 
-				if (change->tp.oldtuple)
+				oldtup = change->data.tp.oldtuple;
+				newtup = change->data.tp.newtuple;
+
+				if (oldtup)
 					oldlen = offsetof(ReorderBufferTupleBuf, data)
-						+ change->tp.oldtuple->tuple.t_len
+						+ oldtup->tuple.t_len
 						- offsetof(HeapTupleHeaderData, t_bits);
 
-				if (change->tp.newtuple)
+				if (newtup)
 					newlen = offsetof(ReorderBufferTupleBuf, data)
-						+ change->tp.newtuple->tuple.t_len
+						+ newtup->tuple.t_len
 						- offsetof(HeapTupleHeaderData, t_bits);
 
 				sz += oldlen;
@@ -2051,26 +2031,27 @@ ReorderBufferSerializeChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
 
 				if (oldlen)
 				{
-					memcpy(data, change->tp.oldtuple, oldlen);
+					memcpy(data, oldtup, oldlen);
 					data += oldlen;
-					Assert(&change->tp.oldtuple->header == change->tp.oldtuple->tuple.t_data);
 				}
 
 				if (newlen)
 				{
-					memcpy(data, change->tp.newtuple, newlen);
+					memcpy(data, newtup, newlen);
 					data += newlen;
-					Assert(&change->tp.newtuple->header == change->tp.newtuple->tuple.t_data);
 				}
 				break;
 			}
 		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 			{
+				Snapshot	snap;
 				char	   *data;
 
+				snap = change->data.snapshot;
+
 				sz += sizeof(SnapshotData) +
-					sizeof(TransactionId) * change->snapshot->xcnt +
-					sizeof(TransactionId) * change->snapshot->subxcnt
+					sizeof(TransactionId) * snap->xcnt +
+					sizeof(TransactionId) * snap->subxcnt
 					;
 
 				/* make sure we have enough space */
@@ -2079,21 +2060,21 @@ ReorderBufferSerializeChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
 				/* might have been reallocated above */
 				ondisk = (ReorderBufferDiskChange *) rb->outbuf;
 
-				memcpy(data, change->snapshot, sizeof(SnapshotData));
+				memcpy(data, snap, sizeof(SnapshotData));
 				data += sizeof(SnapshotData);
 
-				if (change->snapshot->xcnt)
+				if (snap->xcnt)
 				{
-					memcpy(data, change->snapshot->xip,
-						   sizeof(TransactionId) + change->snapshot->xcnt);
-					data += sizeof(TransactionId) + change->snapshot->xcnt;
+					memcpy(data, snap->xip,
+						   sizeof(TransactionId) + snap->xcnt);
+					data += sizeof(TransactionId) + snap->xcnt;
 				}
 
-				if (change->snapshot->subxcnt)
+				if (snap->subxcnt)
 				{
-					memcpy(data, change->snapshot->subxip,
-						   sizeof(TransactionId) + change->snapshot->subxcnt);
-					data += sizeof(TransactionId) + change->snapshot->subxcnt;
+					memcpy(data, snap->subxip,
+						   sizeof(TransactionId) + snap->subxcnt);
+					data += sizeof(TransactionId) + snap->subxcnt;
 				}
 				break;
 			}
@@ -2116,7 +2097,7 @@ ReorderBufferSerializeChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
 						txn->xid)));
 	}
 
-	Assert(ondisk->change.action_internal == change->action_internal);
+	Assert(ondisk->change.action == change->action);
 }
 
 /*
@@ -2271,56 +2252,60 @@ ReorderBufferRestoreChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
 	data += sizeof(ReorderBufferDiskChange);
 
 	/* restore individual stuff */
-	switch ((ReorderBufferChangeTypeInternal) change->action_internal)
+	switch (change->action)
 	{
-		case REORDER_BUFFER_CHANGE_INTERNAL_INSERT:
+		case REORDER_BUFFER_CHANGE_INSERT:
 			/* fall through */
-		case REORDER_BUFFER_CHANGE_INTERNAL_UPDATE:
+		case REORDER_BUFFER_CHANGE_UPDATE:
 			/* fall through */
-		case REORDER_BUFFER_CHANGE_INTERNAL_DELETE:
-			if (change->tp.newtuple)
+		case REORDER_BUFFER_CHANGE_DELETE:
+			if (change->data.tp.newtuple)
 			{
 				Size		len = offsetof(ReorderBufferTupleBuf, data)
 				+((ReorderBufferTupleBuf *) data)->tuple.t_len
 				- offsetof(HeapTupleHeaderData, t_bits);
 
-				change->tp.newtuple = ReorderBufferGetTupleBuf(rb);
-				memcpy(change->tp.newtuple, data, len);
-				change->tp.newtuple->tuple.t_data = &change->tp.newtuple->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->header;
 				data += len;
 			}
 
-			if (change->tp.oldtuple)
+			if (change->data.tp.oldtuple)
 			{
 				Size		len = offsetof(ReorderBufferTupleBuf, data)
 				+((ReorderBufferTupleBuf *) data)->tuple.t_len
 				- offsetof(HeapTupleHeaderData, t_bits);
 
-				change->tp.oldtuple = ReorderBufferGetTupleBuf(rb);
-				memcpy(change->tp.oldtuple, data, len);
-				change->tp.oldtuple->tuple.t_data = &change->tp.oldtuple->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->header;
 				data += len;
 			}
 			break;
 		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 			{
-				Snapshot	oldsnap = (Snapshot) data;
-				Size		size = sizeof(SnapshotData) +
-				sizeof(TransactionId) * oldsnap->xcnt +
-				sizeof(TransactionId) * (oldsnap->subxcnt + 0)
-						   ;
-
-				Assert(change->snapshot != NULL);
-
-				change->snapshot = MemoryContextAllocZero(rb->context, size);
-
-				memcpy(change->snapshot, data, size);
-				change->snapshot->xip = (TransactionId *)
-					(((char *) change->snapshot) + sizeof(SnapshotData));
-				change->snapshot->subxip =
-					change->snapshot->xip + change->snapshot->xcnt + 0;
-				change->snapshot->copied = true;
+				Snapshot	oldsnap;
+				Snapshot	newsnap;
+				Size		size;
+
+				oldsnap = (Snapshot) data;
+
+				size = sizeof(SnapshotData) +
+					sizeof(TransactionId) * oldsnap->xcnt +
+					sizeof(TransactionId) * (oldsnap->subxcnt + 0);
+
+				change->data.snapshot = MemoryContextAllocZero(rb->context, size);
+
+				newsnap = change->data.snapshot;
+
+				memcpy(newsnap, data, size);
+				newsnap->xip = (TransactionId *)
+					(((char *) newsnap) + sizeof(SnapshotData));
+				newsnap->subxip = newsnap->xip + newsnap->xcnt;
+				newsnap->copied = true;
 				break;
 			}
 			/* the base struct contains all the data, easy peasy */
@@ -2464,6 +2449,7 @@ ReorderBufferToastAppendChunk(ReorderBuffer *rb, ReorderBufferTXN *txn,
 							  Relation relation, ReorderBufferChange *change)
 {
 	ReorderBufferToastEnt *ent;
+	ReorderBufferTupleBuf *newtup;
 	bool		found;
 	int32		chunksize;
 	bool		isnull;
@@ -2477,9 +2463,10 @@ ReorderBufferToastAppendChunk(ReorderBuffer *rb, ReorderBufferTXN *txn,
 
 	Assert(IsToastRelation(relation));
 
-	chunk_id = DatumGetObjectId(fastgetattr(&change->tp.newtuple->tuple, 1, desc, &isnull));
+	newtup = change->data.tp.newtuple;
+	chunk_id = DatumGetObjectId(fastgetattr(&newtup->tuple, 1, desc, &isnull));
 	Assert(!isnull);
-	chunk_seq = DatumGetInt32(fastgetattr(&change->tp.newtuple->tuple, 2, desc, &isnull));
+	chunk_seq = DatumGetInt32(fastgetattr(&newtup->tuple, 2, desc, &isnull));
 	Assert(!isnull);
 
 	ent = (ReorderBufferToastEnt *)
@@ -2505,7 +2492,7 @@ ReorderBufferToastAppendChunk(ReorderBuffer *rb, ReorderBufferTXN *txn,
 		elog(ERROR, "got sequence entry %d for toast chunk %u instead of seq %d",
 			 chunk_seq, chunk_id, ent->last_chunk_seq + 1);
 
-	chunk = DatumGetPointer(fastgetattr(&change->tp.newtuple->tuple, 3, desc, &isnull));
+	chunk = DatumGetPointer(fastgetattr(&newtup->tuple, 3, desc, &isnull));
 	Assert(!isnull);
 
 	/* calculate size so we can allocate the right size at once later */
@@ -2539,10 +2526,11 @@ ReorderBufferToastReplace(ReorderBuffer *rb, ReorderBufferTXN *txn,
 	Datum	   *attrs;
 	bool	   *isnull;
 	bool	   *free;
-	HeapTuple	newtup;
+	HeapTuple	tmphtup;
 	Relation	toast_rel;
 	TupleDesc	toast_desc;
 	MemoryContext oldcontext;
+	ReorderBufferTupleBuf *newtup;
 
 	/* no toast tuples changed */
 	if (txn->toast_hash == NULL)
@@ -2551,7 +2539,7 @@ ReorderBufferToastReplace(ReorderBuffer *rb, ReorderBufferTXN *txn,
 	oldcontext = MemoryContextSwitchTo(rb->context);
 
 	/* we should only have toast tuples in an INSERT or UPDATE */
-	Assert(change->tp.newtuple);
+	Assert(change->data.tp.newtuple);
 
 	desc = RelationGetDescr(relation);
 
@@ -2563,8 +2551,9 @@ ReorderBufferToastReplace(ReorderBuffer *rb, ReorderBufferTXN *txn,
 	isnull = palloc0(sizeof(bool) * desc->natts);
 	free = palloc0(sizeof(bool) * desc->natts);
 
-	heap_deform_tuple(&change->tp.newtuple->tuple, desc,
-					  attrs, isnull);
+	newtup = change->data.tp.newtuple;
+
+	heap_deform_tuple(&newtup->tuple, desc, attrs, isnull);
 
 	for (natt = 0; natt < desc->natts; natt++)
 	{
@@ -2628,10 +2617,14 @@ ReorderBufferToastReplace(ReorderBuffer *rb, ReorderBufferTXN *txn,
 		dlist_foreach(it, &ent->chunks)
 		{
 			bool		isnull;
-			ReorderBufferTupleBuf *tup =
-			dlist_container(ReorderBufferChange, node, it.cur)->tp.newtuple;
-			Pointer		chunk =
-			DatumGetPointer(fastgetattr(&tup->tuple, 3, toast_desc, &isnull));
+			ReorderBufferChange *cchange;
+			ReorderBufferTupleBuf *ctup;
+			Pointer		chunk;
+
+			cchange = dlist_container(ReorderBufferChange, node, it.cur);
+			ctup = cchange->data.tp.newtuple;
+			chunk = DatumGetPointer(
+				fastgetattr(&ctup->tuple, 3, toast_desc, &isnull));
 
 			Assert(!isnull);
 			Assert(!VARATT_IS_EXTERNAL(chunk));
@@ -2665,21 +2658,19 @@ ReorderBufferToastReplace(ReorderBuffer *rb, ReorderBufferTXN *txn,
 	 * passed to the output plugin. We can't directly heap_fill_tuple() into
 	 * the tuplebuf because attrs[] will point back into the current content.
 	 */
-	newtup = heap_form_tuple(desc, attrs, isnull);
-	Assert(change->tp.newtuple->tuple.t_len <= MaxHeapTupleSize);
-	Assert(&change->tp.newtuple->header == change->tp.newtuple->tuple.t_data);
+	tmphtup = heap_form_tuple(desc, attrs, isnull);
+	Assert(newtup->tuple.t_len <= MaxHeapTupleSize);
+	Assert(&newtup->header == newtup->tuple.t_data);
 
-	memcpy(change->tp.newtuple->tuple.t_data,
-		   newtup->t_data,
-		   newtup->t_len);
-	change->tp.newtuple->tuple.t_len = newtup->t_len;
+	memcpy(newtup->tuple.t_data, tmphtup->t_data, tmphtup->t_len);
+	newtup->tuple.t_len = tmphtup->t_len;
 
 	/*
 	 * free resources we won't further need, more persistent stuff will be
 	 * free'd in ReorderBufferToastReset().
 	 */
 	RelationClose(toast_rel);
-	pfree(newtup);
+	pfree(tmphtup);
 	for (natt = 0; natt < desc->natts; natt++)
 	{
 		if (free[natt])

src/include/replication/reorderbuffer.h

@@ -32,12 +32,22 @@ typedef struct ReorderBufferTupleBuf
 	char		data[MaxHeapTupleSize];
 } ReorderBufferTupleBuf;
 
-/* types of the change passed to a 'change' callback */
+/*
+ * Types of the change passed to a 'change' callback.
+ *
+ * For efficiency and simplicity reasons we want to keep Snapshots, CommandIds
+ * and ComboCids in the same list with the user visible INSERT/UPDATE/DELETE
+ * changes. Users of the decoding facilities will never see changes with
+ * *_INTERNAL_* actions.
+ */
 enum ReorderBufferChangeType
 {
 	REORDER_BUFFER_CHANGE_INSERT,
 	REORDER_BUFFER_CHANGE_UPDATE,
-	REORDER_BUFFER_CHANGE_DELETE
+	REORDER_BUFFER_CHANGE_DELETE,
+	REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT,
+	REORDER_BUFFER_CHANGE_INTERNAL_COMMAND_ID,
+	REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID
 };
 
 /*
@@ -51,13 +61,8 @@ typedef struct ReorderBufferChange
 {
 	XLogRecPtr	lsn;
 
-	/* type of change */
-	union
-	{
-		enum ReorderBufferChangeType action;
-		/* do not leak internal enum values to the outside */
-		int			action_internal;
-	};
+	/* The type of change. */
+	enum ReorderBufferChangeType action;
 
 	/*
 	 * Context data for the change, which part of the union is valid depends
@@ -65,7 +70,7 @@ typedef struct ReorderBufferChange
 	 */
 	union
 	{
-		/* old, new tuples when action == *_INSERT|UPDATE|DELETE */
+		/* Old, new tuples when action == *_INSERT|UPDATE|DELETE */
 		struct
 		{
 			/* relation that has been changed */
@@ -76,13 +81,19 @@ typedef struct ReorderBufferChange
 			ReorderBufferTupleBuf *newtuple;
 		} tp;
 
-		/* new snapshot */
+		/* New snapshot, set when action == *_INTERNAL_SNAPSHOT */
 		Snapshot	snapshot;
 
-		/* new command id for existing snapshot in a catalog changing tx */
+		/*
+		 * New command id for existing snapshot in a catalog changing tx. Set
+		 * when action == *_INTERNAL_COMMAND_ID.
+		 */
 		CommandId	command_id;
 
-		/* new cid mapping for catalog changing transaction */
+		/*
+		 * New cid mapping for catalog changing transaction, set when action
+		 * == *_INTERNAL_TUPLECID.
+		 */
 		struct
 		{
 			RelFileNode node;
@@ -91,7 +102,7 @@ typedef struct ReorderBufferChange
 			CommandId	cmax;
 			CommandId	combocid;
 		}			tuplecid;
-	};
+	} data;
 
 	/*
 	 * While in use this is how a change is linked into a transactions,