Applying InnoDB snashot 5.0-ss4007, part 3. Fixes

Bug #41571: MySQL segfaults after innodb recovery

This 5.0 fix will not be pushed into 5.1; a separate fix (from
innodb-5.1-ss4007) will be pushed into 5.1+.

Detailed revision comments:

r4003 | marko | 2009-01-20 16:12:50 +0200 (Tue, 20 Jan 2009) | 10 lines
branches/5.0: rec_set_nth_field(): When the field already is SQL null,
do nothing when it is being changed to SQL null. (Bug #41571)

Normally, MySQL does not pass "do-nothing" updates to the storage engine.
When it does and a column of an InnoDB table that is in ROW_FORMAT=COMPACT
is being updated from NULL to NULL, the InnoDB buffer pool will be corrupted
without this fix.

rb://81 approved by Heikki Tuuri

innobase/include/rem0rec.h

@@ -368,8 +368,9 @@ rec_set_field_extern_bits(
 /*************************************************************** 
 This is used to modify the value of an already existing field in a record.
 The previous value must have exactly the same size as the new value. If len
-is UNIV_SQL_NULL then the field is treated as an SQL null for old-style
-records. For new-style records, len must not be UNIV_SQL_NULL. */
+is UNIV_SQL_NULL then the field is treated as an SQL null.
+For records in ROW_FORMAT=COMPACT (new-style records), len must not be
+UNIV_SQL_NULL unless the field already is SQL null. */
 UNIV_INLINE
 void
 rec_set_nth_field(
@@ -378,11 +379,7 @@ rec_set_nth_field(
 	const ulint*	offsets,/* in: array returned by rec_get_offsets() */
 	ulint		n,	/* in: index number of the field */
 	const void*	data,	/* in: pointer to the data if not SQL null */
-	ulint		len);	/* in: length of the data or UNIV_SQL_NULL.
-				If not SQL null, must have the same
-				length as the previous value.
-				If SQL null, previous value must be
-				SQL null. */
+	ulint		len);	/* in: length of the data or UNIV_SQL_NULL */
 /************************************************************** 
 The following function returns the data size of an old-style physical
 record, that is the sum of field lengths. SQL null fields

innobase/include/rem0rec.ic

@@ -1204,8 +1204,9 @@ rec_get_nth_field_size(
 /*************************************************************** 
 This is used to modify the value of an already existing field in a record.
 The previous value must have exactly the same size as the new value. If len
-is UNIV_SQL_NULL then the field is treated as an SQL null for old-style
-records. For new-style records, len must not be UNIV_SQL_NULL. */
+is UNIV_SQL_NULL then the field is treated as an SQL null.
+For records in ROW_FORMAT=COMPACT (new-style records), len must not be
+UNIV_SQL_NULL unless the field already is SQL null. */
 UNIV_INLINE
 void
 rec_set_nth_field(
@@ -1215,11 +1216,7 @@ rec_set_nth_field(
 	ulint		n,	/* in: index number of the field */
 	const void*	data,	/* in: pointer to the data
 				if not SQL null */
-	ulint		len)	/* in: length of the data or UNIV_SQL_NULL.
-				If not SQL null, must have the same
-				length as the previous value.
-				If SQL null, previous value must be
-				SQL null. */
+	ulint		len)	/* in: length of the data or UNIV_SQL_NULL */
 {
 	byte*	data2;
 	ulint	len2;
@@ -1227,9 +1224,11 @@ rec_set_nth_field(
 	ut_ad(rec);
 	ut_ad(rec_offs_validate(rec, NULL, offsets));
 
-	if (len == UNIV_SQL_NULL) {
-		ut_ad(!rec_offs_comp(offsets));
-		rec_set_nth_field_sql_null(rec, n);
+	if (UNIV_UNLIKELY(len == UNIV_SQL_NULL)) {
+		if (!rec_offs_nth_sql_null(offsets, n)) {
+			ut_a(!rec_offs_comp(offsets));
+			rec_set_nth_field_sql_null(rec, n);
+		}
 
 		return;
 	}