SET DEBUG_SYNC='RESET';
CREATE TABLE t1 (c1 INT PRIMARY KEY, c2 INT, INDEX(c2)) ENGINE = InnoDB;
CREATE TABLE t2 (
c2 INT PRIMARY KEY,
CONSTRAINT t2c2 FOREIGN KEY (c2) REFERENCES t1 (c2))
ENGINE = InnoDB;
DROP INDEX c2 ON t1;
ERROR HY000: Cannot drop index 'c2': needed in a foreign key constraint
DROP TABLE t2;
SET DEBUG_SYNC = 'innodb_after_inplace_alter_table SIGNAL drop WAIT_FOR fk';
DROP INDEX c2 ON t1;
# Establish session con1 (user=root)
# Session con1
SET DEBUG_SYNC = 'now WAIT_FOR drop';
CREATE TABLE t2 (
c2 INT PRIMARY KEY,
CONSTRAINT t2c2 FOREIGN KEY (c2) REFERENCES t1 (c2))
ENGINE = InnoDB;
# Establish session con2 (user=root)
# After WL#6049 CREATE TABLE t2 must be blocked while trying
# to acquire exclusive metadata lock on t1.
SET DEBUG_SYNC = 'now SIGNAL fk';
# Switching to connection con1.
# So no chance for CREATE TABLE t2 to sneak before DROP INDEX
# is committed in and succeed.
/* reap */ CREATE TABLE t2 ...
ERROR HY000: Failed to add the foreign key constraint. Missing index for constraint 't2c2' in the referenced table 't1'
# Session default
/* reap */ DROP INDEX c2 ON t1;
CREATE TABLE t2 (
c2 INT PRIMARY KEY,
CONSTRAINT t2c2 FOREIGN KEY (c2) REFERENCES t1 (c2))
ENGINE = InnoDB;
ERROR HY000: Failed to add the foreign key constraint. Missing index for constraint 't2c2' in the referenced table 't1'
SET DEBUG_SYNC='RESET';
DROP TABLE t1;