MDEV-12827 Assertion failure when reporting duplicate key error in online table rebuild

row_log_table_apply_insert_low(), row_log_table_apply_update():
When reporting the error_key_num, only count the clustered index
if it corresponds to a key in the SQL layer.

The assertion failure was probably introduced by the (incomplete)
MySQL 5.6.28 bug fix
Bug #21364096 THE BOGUS DUPLICATE KEY ERROR IN ONLINE DDL
WITH INCORRECT KEY NAME
which we are improving.

Side note: the fix was incorrectly merged to MySQL 5.7.10;
incorrect key names will continue to be reported in MySQL 5.7.

mysql-test/suite/innodb/r/innodb-index-debug.result

@@ -67,3 +67,25 @@ alter table t1 force, algorithm=inplace;
 ERROR HY000: Out of memory; check if mysqld or some other process uses all available memory; if not, you may have to use 'ulimit' to allow mysqld to use more memory or you can add more swap space
 SET DEBUG_DBUG = @saved_debug_dbug;
 drop table t1, t480;
+#
+# MDEV-12827 Assertion failure when reporting duplicate key error
+# in online table rebuild
+#
+CREATE TABLE t1 (j INT UNIQUE, i INT UNIQUE) ENGINE=InnoDB;
+SET DEBUG_SYNC='row_log_table_apply1_before SIGNAL built WAIT_FOR log';
+ALTER TABLE t1 DROP j, FORCE;
+SET DEBUG_SYNC='now WAIT_FOR built';
+INSERT INTO t1 (i) VALUES (0),(0);
+ERROR 23000: Duplicate entry '0' for key 'i'
+SET DEBUG_SYNC='now SIGNAL log';
+ERROR 23000: Duplicate entry '0' for key 'i'
+SET DEBUG_SYNC='row_log_table_apply1_before SIGNAL built2 WAIT_FOR log2';
+ALTER TABLE t1 DROP j, FORCE;
+SET DEBUG_SYNC='now WAIT_FOR built2';
+INSERT INTO t1 (i) VALUES (0),(1);
+UPDATE t1 SET i=0;
+ERROR 23000: Duplicate entry '0' for key 'i'
+SET DEBUG_SYNC='now SIGNAL log2';
+ERROR 23000: Duplicate entry '0' for key 'i'
+SET DEBUG_SYNC='RESET';
+DROP TABLE t1;

mysql-test/suite/innodb/t/innodb-index-debug.test

@@ -1,7 +1,6 @@
 -- source include/have_debug.inc
 -- source include/have_innodb.inc
-
+-- source include/have_debug_sync.inc
-let $MYSQLD_DATADIR= `select @@datadir`;
 
 let $per_table=`select @@innodb_file_per_table`;
 let $format=`select @@innodb_file_format`;
@@ -82,3 +81,42 @@ SET DEBUG_DBUG = '+d,innobase_tmpfile_creation_failure';
 alter table t1 force, algorithm=inplace;
 SET DEBUG_DBUG = @saved_debug_dbug;
 drop table t1, t480;
+
+--echo #
+--echo # MDEV-12827 Assertion failure when reporting duplicate key error
+--echo # in online table rebuild
+--echo #
+
+CREATE TABLE t1 (j INT UNIQUE, i INT UNIQUE) ENGINE=InnoDB;
+--connect (con1,localhost,root,,test)
+SET DEBUG_SYNC='row_log_table_apply1_before SIGNAL built WAIT_FOR log';
+--send
+ALTER TABLE t1 DROP j, FORCE;
+
+--connection default
+SET DEBUG_SYNC='now WAIT_FOR built';
+--error ER_DUP_ENTRY
+INSERT INTO t1 (i) VALUES (0),(0);
+SET DEBUG_SYNC='now SIGNAL log';
+
+--connection con1
+--error ER_DUP_ENTRY
+reap;
+SET DEBUG_SYNC='row_log_table_apply1_before SIGNAL built2 WAIT_FOR log2';
+--send
+ALTER TABLE t1 DROP j, FORCE;
+
+--connection default
+SET DEBUG_SYNC='now WAIT_FOR built2';
+INSERT INTO t1 (i) VALUES (0),(1);
+--error ER_DUP_ENTRY
+UPDATE t1 SET i=0;
+SET DEBUG_SYNC='now SIGNAL log2';
+
+--connection con1
+--error ER_DUP_ENTRY
+reap;
+--disconnect con1
+--connection default
+SET DEBUG_SYNC='RESET';
+DROP TABLE t1;

storage/innobase/row/row0log.cc

@@ -1520,13 +1520,10 @@ row_log_table_apply_insert_low(
 		return(error);
 	}
 
-	do {
+	ut_ad(dict_index_is_clust(index));
-		n_index++;
-
-		if (!(index = dict_table_get_next_index(index))) {
-			break;
-		}
 
+	for (n_index += index->type != DICT_CLUSTERED;
+	     (index = dict_table_get_next_index(index)); n_index++) {
 		if (index->type & DICT_FTS) {
 			continue;
 		}
@@ -1536,12 +1533,13 @@ row_log_table_apply_insert_low(
 			flags, BTR_MODIFY_TREE,
 			index, offsets_heap, heap, entry, trx_id, thr);
 
-		/* Report correct index name for duplicate key error. */
+		if (error != DB_SUCCESS) {
-		if (error == DB_DUPLICATE_KEY) {
+			if (error == DB_DUPLICATE_KEY) {
-			thr_get_trx(thr)->error_key_num = n_index;
+				thr_get_trx(thr)->error_key_num = n_index;
+			}
+			break;
 		}
-
+	}
-	} while (error == DB_SUCCESS);
 
 	return(error);
 }
@@ -2120,17 +2118,16 @@ func_exit_committed:
 		dtuple_big_rec_free(big_rec);
 	}
 
-	while ((index = dict_table_get_next_index(index)) != NULL) {
+	for (n_index += index->type != DICT_CLUSTERED;
-		if (error != DB_SUCCESS) {
+	     (index = dict_table_get_next_index(index)); n_index++) {
-			break;
-		}
-
-		n_index++;
-
 		if (index->type & DICT_FTS) {
 			continue;
 		}
 
+		if (error != DB_SUCCESS) {
+			break;
+		}
+
 		if (!row_upd_changes_ord_field_binary(
 			    index, update, thr, old_row, NULL)) {
 			continue;

storage/xtradb/row/row0log.cc

@@ -1520,13 +1520,10 @@ row_log_table_apply_insert_low(
 		return(error);
 	}
 
-	do {
+	ut_ad(dict_index_is_clust(index));
-		n_index++;
-
-		if (!(index = dict_table_get_next_index(index))) {
-			break;
-		}
 
+	for (n_index += index->type != DICT_CLUSTERED;
+	     (index = dict_table_get_next_index(index)); n_index++) {
 		if (index->type & DICT_FTS) {
 			continue;
 		}
@@ -1536,12 +1533,13 @@ row_log_table_apply_insert_low(
 			flags, BTR_MODIFY_TREE,
 			index, offsets_heap, heap, entry, trx_id, thr);
 
-		/* Report correct index name for duplicate key error. */
+		if (error != DB_SUCCESS) {
-		if (error == DB_DUPLICATE_KEY) {
+			if (error == DB_DUPLICATE_KEY) {
-			thr_get_trx(thr)->error_key_num = n_index;
+				thr_get_trx(thr)->error_key_num = n_index;
+			}
+			break;
 		}
-
+	}
-	} while (error == DB_SUCCESS);
 
 	return(error);
 }
@@ -2120,17 +2118,16 @@ func_exit_committed:
 		dtuple_big_rec_free(big_rec);
 	}
 
-	while ((index = dict_table_get_next_index(index)) != NULL) {
+	for (n_index += index->type != DICT_CLUSTERED;
-		if (error != DB_SUCCESS) {
+	     (index = dict_table_get_next_index(index)); n_index++) {
-			break;
-		}
-
-		n_index++;
-
 		if (index->type & DICT_FTS) {
 			continue;
 		}
 
+		if (error != DB_SUCCESS) {
+			break;
+		}
+
 		if (!row_upd_changes_ord_field_binary(
 			    index, update, thr, old_row, NULL)) {
 			continue;