MDEV-25642 InnoDB rename table copy DDL fails while dropping the table

When doing a ALTER TABLE ... RENAME, MariaDB doesn't rename original table to #sql-backup, which it does in other cases, but insteads drops the original table directly. However this optimization doesn't work in case of InnoDB table with a foreign key constraint. During copy algorithm, InnoDB fails to rename the foreign key constraint(MDEV-25855). With this optimisation, InnoDB also fails to drop the original table because the table has FOREIGN Key constraint exist in INNODB_SYS_FOREIGN table. This leads to orphan .ibd file in InnoDB dictionary. so disabling this optimization when FK is involved. Reviewer: monty@mariadb.org

Author: Thirunarayanan

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

@@ -206,3 +206,18 @@ c0123456789012345678 int,
 FOREIGN KEY (a012345678901234567,c0123456789012345678,b) REFERENCES tx (x1,x2,x3)
 ) ENGINE=InnoDB;
 ERROR HY000: Can't create table `test`.`t1` (errno: 150 "Foreign key constraint is incorrectly formed")
+#
+# MDEV-25642 InnoDB rename table copy DDL fails
+#	while dropping the table
+#
+call mtr.add_suppression("InnoDB: In ALTER TABLE `test`.`t1` has or is referenced in foreign key constraints which are not compatible with the new table definition.");
+CREATE TABLE t1 (a VARCHAR(10) NOT NULL PRIMARY KEY) ENGINE=InnoDB;
+CREATE TABLE t1_fk (a VARCHAR(40), KEY a (a), FULLTEXT KEY(a), CONSTRAINT fk FOREIGN KEY(a) REFERENCES t1 (a) ON UPDATE CASCADE) ENGINE=InnoDB;
+ALTER TABLE t1 RENAME TO tm1, ALGORITHM=COPY;
+SELECT * FROM INFORMATION_SCHEMA.INNODB_SYS_FOREIGN;
+ID	FOR_NAME	REF_NAME	N_COLS	TYPE
+test/fk	test/t1_fk	test/t1	1	4
+SET FOREIGN_KEY_CHECKS=0;
+CREATE TABLE t1 (c1 BIGINT NOT NULL, c2 BIGINT NOT NULL, PRIMARY KEY(c1), UNIQUE KEY(c2)) ENGINE=MEMORY;
+ALTER TABLE t1 ENGINE=InnoDB, ALGORITHM=COPY;
+DROP TABLE t1, tm1, t1_fk;

mysql-test/suite/innodb/t/innodb-fk.test

@@ -244,3 +244,19 @@ CREATE TABLE t1 (
  c0123456789012345678 int,
  FOREIGN KEY (a012345678901234567,c0123456789012345678,b) REFERENCES tx (x1,x2,x3)
 ) ENGINE=InnoDB;
+
+--echo #
+--echo # MDEV-25642 InnoDB rename table copy DDL fails
+--echo #	while dropping the table
+--echo #
+call mtr.add_suppression("InnoDB: In ALTER TABLE `test`.`t1` has or is referenced in foreign key constraints which are not compatible with the new table definition.");
+
+CREATE TABLE t1 (a VARCHAR(10) NOT NULL PRIMARY KEY) ENGINE=InnoDB;
+CREATE TABLE t1_fk (a VARCHAR(40), KEY a (a), FULLTEXT KEY(a), CONSTRAINT fk FOREIGN KEY(a) REFERENCES t1 (a) ON UPDATE CASCADE) ENGINE=InnoDB;
+ALTER TABLE t1 RENAME TO tm1, ALGORITHM=COPY;
+SELECT * FROM INFORMATION_SCHEMA.INNODB_SYS_FOREIGN;
+# Enable SET FOREIGN_KEY_CHECKS after fixing MDEV-25885
+SET FOREIGN_KEY_CHECKS=0;
+CREATE TABLE t1 (c1 BIGINT NOT NULL, c2 BIGINT NOT NULL, PRIMARY KEY(c1), UNIQUE KEY(c2)) ENGINE=MEMORY;
+ALTER TABLE t1 ENGINE=InnoDB, ALGORITHM=COPY;
+DROP TABLE t1, tm1, t1_fk;

sql/sql_table.cc

@@ -11009,7 +11009,12 @@ do_continue:;
  DBUG_PRINT("info", ("is_table_renamed: %d engine_changed: %d",
  alter_ctx.is_table_renamed(), engine_changed));
 
- if (!alter_ctx.is_table_renamed())
+ /*
+ InnoDB cannot use the rename optimization when foreign key
+ constraint is involved because InnoDB fails to drop the
+ parent table due to foreign key constraint
+ */
+ if (!alter_ctx.is_table_renamed() || alter_ctx.fk_error_if_delete_row)
  {
  backup_name.length= my_snprintf(backup_name_buff, sizeof(backup_name_buff),
  "%s-backup-%lx-%llx", tmp_file_prefix,
@@ -11044,7 +11049,7 @@ do_continue:;
  (void) quick_rm_table(thd, new_db_type, &alter_ctx.new_db,
  &alter_ctx.tmp_name, FN_IS_TMP);
 
- if (!alter_ctx.is_table_renamed())
+ if (!alter_ctx.is_table_renamed() || alter_ctx.fk_error_if_delete_row)
  {
  // Restore the backup of the original table to the old name.
  (void) mysql_rename_table(old_db_type, &alter_ctx.db, &backup_name,