Bug#14554000 CRASH IN PAGE_REC_GET_NTH_CONST(NTH=0) DURING COMPRESSED

PAGE SPLIT

page_rec_get_nth_const(): Map nth==0 to the page infimum.

btr_compress(adjust=TRUE): Add a debug assertion for nth>0. The cursor
should never be positioned on the page infimum.

btr_index_page_validate(): Add test instrumentation for checking the
return values of page_rec_get_nth_const() during CHECK TABLE, and for
checking that the page directory slot 0 always contains only one
record, the predefined page infimum record.

page_cur_delete_rec(), page_delete_rec_list_end(): Add debug
assertions guarding against accessing the page slot 0.

page_copy_rec_list_start(): Clarify a comment about ret_pos==0.

rb:1248 approved by Jimmy Yang

storage/innodb_plugin/ChangeLog

+2012-08-29	The InnoDB Team
+
+	* btr/btr0btr.c, page/page0cur.c, page/page0page.c:
+	Fix Bug#14554000 CRASH IN PAGE_REC_GET_NTH_CONST(NTH=0)
+	DURING COMPRESSED PAGE SPLIT
+
 2012-08-16	The InnoDB Team
 
 	* btr/btr0cur.c:

storage/innodb_plugin/btr/btr0btr.c

@@ -3241,6 +3241,7 @@ btr_compress(
 
 	if (adjust) {
 		nth_rec = page_rec_get_n_recs_before(btr_cur_get_rec(cursor));
+		ut_ad(nth_rec > 0);
 	}
 
 	/* Decide the page to which we try to merge and which will inherit
@@ -3476,6 +3477,7 @@ func_exit:
 	mem_heap_free(heap);
 
 	if (adjust) {
+		ut_ad(nth_rec > 0);
 		btr_cur_position(
 			index,
 			page_rec_get_nth(merge_block->frame, nth_rec),
@@ -3988,8 +3990,22 @@ btr_index_page_validate(
 {
 	page_cur_t	cur;
 	ibool		ret	= TRUE;
+#ifndef DBUG_OFF
+	ulint		nth	= 1;
+#endif /* !DBUG_OFF */
 
 	page_cur_set_before_first(block, &cur);
+
+	/* Directory slot 0 should only contain the infimum record. */
+	DBUG_EXECUTE_IF("check_table_rec_next",
+			ut_a(page_rec_get_nth_const(
+				     page_cur_get_page(&cur), 0)
+			     == cur.rec);
+			ut_a(page_dir_slot_get_n_owned(
+				     page_dir_get_nth_slot(
+					     page_cur_get_page(&cur), 0))
+			     == 1););
+
 	page_cur_move_to_next(&cur);
 
 	for (;;) {
@@ -4003,6 +4019,16 @@ btr_index_page_validate(
 			return(FALSE);
 		}
 
+		/* Verify that page_rec_get_nth_const() is correctly
+		retrieving each record. */
+		DBUG_EXECUTE_IF("check_table_rec_next",
+				ut_a(cur.rec == page_rec_get_nth_const(
+					     page_cur_get_page(&cur),
+					     page_rec_get_n_recs_before(
+						     cur.rec)));
+				ut_a(nth++ == page_rec_get_n_recs_before(
+					     cur.rec)););
+
 		page_cur_move_to_next(&cur);
 	}
 

storage/innodb_plugin/page/page0cur.c

@@ -1902,6 +1902,7 @@ page_cur_delete_rec(
 
 	/* Save to local variables some data associated with current_rec */
 	cur_slot_no = page_dir_find_owner_slot(current_rec);
+	ut_ad(cur_slot_no > 0);
 	cur_dir_slot = page_dir_get_nth_slot(page, cur_slot_no);
 	cur_n_owned = page_dir_slot_get_n_owned(cur_dir_slot);
 

storage/innodb_plugin/page/page0page.c

@@ -795,8 +795,8 @@ zip_reorganize:
 			/* Before copying, "ret" was the predecessor
 			of the predefined supremum record.  If it was
 			the predefined infimum record, then it would
-			still be the infimum.  Thus, the assertion
-			ut_a(ret_pos > 0) would fail here. */
+			still be the infimum, and we would have
+			ret_pos == 0. */
 
 			if (UNIV_UNLIKELY
 			    (!page_zip_reorganize(new_block, index, mtr))) {
@@ -1051,6 +1051,7 @@ page_delete_rec_list_end(
 
 		n_owned = rec_get_n_owned_new(rec2) - count;
 		slot_index = page_dir_find_owner_slot(rec2);
+		ut_ad(slot_index > 0);
 		slot = page_dir_get_nth_slot(page, slot_index);
 	} else {
 		rec_t*	rec2	= rec;
@@ -1066,6 +1067,7 @@ page_delete_rec_list_end(
 
 		n_owned = rec_get_n_owned_old(rec2) - count;
 		slot_index = page_dir_find_owner_slot(rec2);
+		ut_ad(slot_index > 0);
 		slot = page_dir_get_nth_slot(page, slot_index);
 	}
 
@@ -1492,6 +1494,10 @@ page_rec_get_nth_const(
 	ulint			n_owned;
 	const rec_t*		rec;
 
+	if (nth == 0) {
+		return(page_get_infimum_rec(page));
+	}
+
 	ut_ad(nth < UNIV_PAGE_SIZE / (REC_N_NEW_EXTRA_BYTES + 1));
 
 	for (i = 0;; i++) {