Attempt to fix alignment problem in multixact

vbwagner · vbwagner · commit 1c384530f7c5 · 2016-10-24T17:58:54.000+03:00
diff --git a/src/backend/access/transam/multixact.c b/src/backend/access/transam/multixact.c
@@ -117,8 +117,8 @@
 /*
  * The situation for members is a bit more complex: we store one byte of
  * additional flag bits for each TransactionId.  To do this without getting
- * into alignment issues, we store four bytes of flags, and then the
- * corresponding 4 Xids.  Each such 5-word (20-byte) set we call a "group", and
+ * into alignment issues, we store eight bytes of flags, and then the
+ * corresponding 8 Xids.  Each such 9-word (20-byte) set we call a "group", and
  * are stored as a whole in pages.  Thus, with 8kB BLCKSZ, we keep 409 groups
  * per page.  This wastes 12 bytes per page, but that's OK -- simplicity (and
  * performance) trumps space efficiency here.
@@ -132,7 +132,7 @@
 #define MXACT_MEMBER_XACT_BITMASK	((1 << MXACT_MEMBER_BITS_PER_XACT) - 1)
 
 /* how many full bytes of flags are there in a group? */
-#define MULTIXACT_FLAGBYTES_PER_GROUP		4
+#define MULTIXACT_FLAGBYTES_PER_GROUP	 	8	
 #define MULTIXACT_MEMBERS_PER_MEMBERGROUP	\
 	(MULTIXACT_FLAGBYTES_PER_GROUP * MXACT_MEMBER_FLAGS_PER_BYTE)
 /* size in bytes of a complete group */
@@ -900,6 +900,7 @@ RecordNewMultiXact(MultiXactId multi, MultiXactOffset offset,
 		memberptr = (TransactionId *)
 			(MultiXactMemberCtl->shared->page_buffer[slotno] + memberoff);
 
+
 		*memberptr = members[i].xid;
 
 		flagsptr = (uint32 *)
