From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sun, 25 Mar 2001 22:40:58 +0000 (+0000)
Subject: Improve comments for xlog item size #defines.
X-Git-Url: http://waps.l3s.uni-hannover.de/gitweb/?a=commitdiff_plain;h=f9702a9068715c89da42a1a77156ba068a05b5c7;p=users%2Fbernd%2Fpostgres.git

Improve comments for xlog item size #defines.
---

diff --git a/src/include/access/htup.h b/src/include/access/htup.h
index a2125e469e..f19f7a9541 100644
--- a/src/include/access/htup.h
+++ b/src/include/access/htup.h
@@ -83,6 +83,11 @@ typedef HeapTupleHeaderData *HeapTupleHeader;
 
 /*
  * All what we need to find changed tuple (18 bytes)
+ *
+ * NB: on most machines, sizeof(xl_heaptid) will include some trailing pad
+ * bytes for alignment.  We don't want to store the pad space in the XLOG,
+ * so use SizeOfHeapTid for space calculations.  Similar comments apply for
+ * the other xl_FOO structs.
  */
 typedef struct xl_heaptid
 {
@@ -90,13 +95,15 @@ typedef struct xl_heaptid
 	ItemPointerData tid;		/* changed tuple id */
 } xl_heaptid;
 
+#define SizeOfHeapTid		(offsetof(xl_heaptid, tid) + SizeOfIptrData)
+
 /* This is what we need to know about delete */
 typedef struct xl_heap_delete
 {
 	xl_heaptid	target;			/* deleted tuple id */
 } xl_heap_delete;
 
-#define SizeOfHeapDelete	(offsetof(xl_heaptid, tid) + SizeOfIptrData)
+#define SizeOfHeapDelete	(offsetof(xl_heap_delete, target) + SizeOfHeapTid)
 
 typedef struct xl_heap_header
 {
@@ -115,14 +122,14 @@ typedef struct xl_heap_insert
 	/* xl_heap_header & TUPLE DATA FOLLOWS AT END OF STRUCT */
 } xl_heap_insert;
 
-#define SizeOfHeapInsert	(offsetof(xl_heaptid, tid) + SizeOfIptrData)
+#define SizeOfHeapInsert	(offsetof(xl_heap_insert, target) + SizeOfHeapTid)
 
 /* This is what we need to know about update|move */
 typedef struct xl_heap_update
 {
 	xl_heaptid	target;			/* deleted tuple id */
 	ItemPointerData newtid;		/* new inserted tuple id */
-	/* NEW TUPLE xl_heap_header (XMIN & XMAX FOR MOVE OP) */
+	/* NEW TUPLE xl_heap_header (PLUS xmax & xmin IF MOVE OP) */
 	/* and TUPLE DATA FOLLOWS AT END OF STRUCT */
 } xl_heap_update;