Bug#14621190: HA_INNOBASE::INDEX_NEXT SKIPS A RECORD IF PREVIOUS

INDEX_READ_MAP HAD NO MATCH

If index_read_map is called for exact search and no matching records
exists it will position the cursor on the next record, but still having the
relative position to BTR_PCUR_ON.
This will make a call for index_next to read yet another next record,
instead of returning the record the cursor points to.

Fixed by setting pcur->rel_pos = BTR_PCUR_BEFORE if an exact
[prefix] search is done, but failed.

Also avoids optimistic restoration if rel_pos != BTR_PCUR_ON,
since btr_cur may be different than old_rec.

rb#3324, approved by Marko and Jimmy

mysql-test/suite/innodb/r/innodb_bug13510739.result

@@ -6,5 +6,5 @@ HANDLER bug13510739 READ `primary` = (2);
 c
 HANDLER bug13510739 READ `primary` NEXT;
 c
-4
+3
 DROP TABLE bug13510739;

storage/innobase/btr/btr0pcur.c

@@ -273,13 +273,15 @@ btr_pcur_restore_position_func(
 
 	if (UNIV_LIKELY(latch_mode == BTR_SEARCH_LEAF)
 	    || UNIV_LIKELY(latch_mode == BTR_MODIFY_LEAF)) {
-		/* Try optimistic restoration */
+		/* Try optimistic restoration if cursor is expected to be
+		positioned on the same btr record as before (BTR_PCUR_ON). */
 
-		if (UNIV_LIKELY(buf_page_optimistic_get(
+		if (cursor->rel_pos == BTR_PCUR_ON
+		    && buf_page_optimistic_get(
 					latch_mode,
 					cursor->block_when_stored,
 					cursor->modify_clock,
-					file, line, mtr))) {
+					file, line, mtr)) {
 			cursor->pos_state = BTR_PCUR_IS_POSITIONED;
 
 			buf_block_dbg_add_level(
@@ -287,7 +289,7 @@ btr_pcur_restore_position_func(
 				dict_index_is_ibuf(index)
 				? SYNC_IBUF_TREE_NODE : SYNC_TREE_NODE);
 
-			if (cursor->rel_pos == BTR_PCUR_ON) {
+			{
 #ifdef UNIV_DEBUG
 				const rec_t*	rec;
 				const ulint*	offsets1;
@@ -312,8 +314,6 @@ btr_pcur_restore_position_func(
 #endif /* UNIV_DEBUG */
 				return(TRUE);
 			}
-
-			return(FALSE);
 		}
 	}
 

storage/innobase/row/row0sel.c

@@ -3116,6 +3116,13 @@ sel_restore_position_for_mysql(
 		return(TRUE);
 	}
 
+	/* success can only be TRUE for BTR_PCUR_ON! */
+	ut_ad(!success);
+
+	/* BTR_PCUR_BEFORE -> the position is now set to the record before
+	pcur->old_rec.
+	BTR_PCUR_AFTER-> positioned to record after pcur->old_rec. */
+
 	if (relative_position == BTR_PCUR_AFTER
 	    || relative_position == BTR_PCUR_AFTER_LAST_IN_TREE) {
 
@@ -4120,6 +4127,14 @@ wrong_offs:
 
 			btr_pcur_store_position(pcur, &mtr);
 
+			/* The found record was not a match, but may be used
+			as NEXT record (index_next). Set the relative position
+			to BTR_PCUR_BEFORE, to reflect that the position of
+			the persistent cursor is before the found/stored row
+			(pcur->old_rec). */
+			ut_ad(pcur->rel_pos == BTR_PCUR_ON);
+			pcur->rel_pos = BTR_PCUR_BEFORE;
+
 			err = DB_RECORD_NOT_FOUND;
 			/* ut_print_name(stderr, index->name);
 			fputs(" record not found 3\n", stderr); */
@@ -4159,6 +4174,14 @@ wrong_offs:
 
 			btr_pcur_store_position(pcur, &mtr);
 
+			/* The found record was not a match, but may be used
+			as NEXT record (index_next). Set the relative position
+			to BTR_PCUR_BEFORE, to reflect that the position of
+			the persistent cursor is before the found/stored row
+			(pcur->old_rec). */
+			ut_ad(pcur->rel_pos == BTR_PCUR_ON);
+			pcur->rel_pos = BTR_PCUR_BEFORE;
+
 			err = DB_RECORD_NOT_FOUND;
 			/* ut_print_name(stderr, index->name);
 			fputs(" record not found 4\n", stderr); */
@@ -4736,6 +4759,7 @@ normal_return:
 	if (prebuilt->n_fetch_cached > 0) {
 		row_sel_pop_cached_row_for_mysql(buf, prebuilt);
 
+		DEBUG_SYNC_C("row_search_cached_row");
 		err = DB_SUCCESS;
 	}