Fix minor 9.4-only bug in logical decoding.

tglsfdc · tglsfdc · commit 10ad15f48ab1 · 2016-09-01T11:45:16.000-04:00
The 9.4 version of log_heap_update() stores the full length of the old_key_tuple in xlhdr.t_len, rather than the length less offsetof(HeapTupleHeaderData, t_bits) as is customary elsewhere. DecodeUpdate() was expecting the usual definition, which caused it to copy 23 bytes too much out of the WAL-file buffer. Most of the time that's harmless, although Valgrind on buildfarm member skink has been complaining about it, and there was one actual SIGSEGV on curculio that might have been caused by this. The reconstructed key tuple would also have an over-length t_len, though offhand I do not see how that could cause any visible problem. The problem seems to have disappeared in the 9.5 WAL format changes (commit 2c03216), so we only need to fix 9.4. Discussion: <11035.1469058247@sss.pgh.pa.us>
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
@@ -702,16 +702,16 @@ DecodeUpdate(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 		memcpy(&xlhdr, data, sizeof(xlhdr));
 		data += offsetof(xl_heap_header_len, header);
 
-		datalen = xlhdr.t_len + SizeOfHeapHeader;
-		tuplelen = xlhdr.t_len;
+		/* t_len is inconsistent with other cases, see log_heap_update */
+		tuplelen = xlhdr.t_len - offsetof(HeapTupleHeaderData, t_bits);
+		datalen = tuplelen + SizeOfHeapHeader;
 
 		change->data.tp.oldtuple =
 			ReorderBufferGetTupleBuf(ctx->reorder, tuplelen);
 
 		DecodeXLogTuple(data, datalen, change->data.tp.oldtuple);
 #ifdef NOT_USED
-		data += SizeOfHeapHeader;
-		data += xlhdr.t_len;
+		data += datalen;
 #endif
 	}
 
