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connect stop_purge,localhost,root;
START TRANSACTION WITH CONSISTENT SNAPSHOT;
connect con1,localhost,root,,;
connect con2,localhost,root,,;
connect con3,localhost,root,,;
connection default;
CREATE TABLE t1 (id INT PRIMARY KEY) ENGINE=InnoDB STATS_PERSISTENT=0;
INSERT INTO t1 (id) VALUES (1);
# Simplest scenario:
# <con1, S, granted>,
# <con1, S, granted>, <con2, X, waiting for con1>,
# Before MDEV-34877:
# <con1, S, granted>, <con2, X, waiting for con1>, <con1, X, waiting for con1>
# After MDEV-34877:
# <con1, S, granted>, <con1, X, granted>, <con2, X, waiting for con1>
# Expected: instead of deadlocking, the con1's request should ingore con2's
connection con1;
BEGIN;
SELECT * FROM t1 LOCK IN SHARE MODE;
id
1
connection con2;
BEGIN;
SET DEBUG_SYNC = 'lock_wait_before_suspend SIGNAL con2_will_wait';
SELECT * FROM t1 FOR UPDATE;
connection con1;
SET DEBUG_SYNC = 'now WAIT_FOR con2_will_wait';
SELECT * FROM t1 FOR UPDATE;
id
1
COMMIT;
connection con2;
id
1
COMMIT;
# The scenario when we bypass X<-S pair:
# <con1, S, granted>,
# <con1, S, granted>, <con2, X, waiting for con1>,
# <con1, S, granted>, <con2, X, waiting for con1>, <con3, S, waiting for con2>
# <con1, S, granted>, <con1, X, granted>, <con2, X, waiting for con1>, <con3, S, waiting for con2>
connection con1;
BEGIN;
SELECT * FROM t1 LOCK IN SHARE MODE;
id
1
connection con2;
BEGIN;
SET DEBUG_SYNC = 'lock_wait_before_suspend SIGNAL con2_will_wait';
SELECT * FROM t1 FOR UPDATE;
connection con3;
SET DEBUG_SYNC = 'now WAIT_FOR con2_will_wait';
BEGIN;
SET DEBUG_SYNC = 'lock_wait_before_suspend SIGNAL con3_will_wait';
SELECT * FROM t1 LOCK IN SHARE MODE;;
connection con1;
SET DEBUG_SYNC = 'now WAIT_FOR con3_will_wait';
SELECT * FROM t1 FOR UPDATE;
id
1
COMMIT;
connection con2;
id
1
COMMIT;
connection con3;
id
1
COMMIT;
# A variant of the above scenario:
# <con1, X REC_NOT_GAP, granted>,
# <con1, X REC_NOT_GAP, granted>, <con2, S, waiting for con1>,
# <con1, X REC_NOT_GAP, granted>, <con2, S, waiting for con1>, <con1, INSERT INTENTION, waiting for con1>
# Expected: a deadlock, as INSERT INTENTION should not overtake locks on gap, to not slice them
connection con1;
BEGIN;
SELECT * FROM t1 WHERE id=1 FOR UPDATE;
id
1
connection con2;
BEGIN;
SET DEBUG_SYNC = 'lock_wait_start SIGNAL con2_will_wait';
SELECT * FROM t1 LOCK IN SHARE MODE;
connection con1;
SET DEBUG_SYNC = 'now WAIT_FOR con2_will_wait';
INSERT INTO t1 VALUES (0);
ROLLBACK;
connection con2;
ERROR 40001: Deadlock found when trying to get lock; try restarting transaction
COMMIT;
# More complicated scenario:
# <con1, S, granted>,
# <con1, S, granted>, <con2, S REC_NOT_GAP, granted>,
# <con1, S, granted>, <con2, S REC_NOT_GAP, granted>, <con3, X, waiting for con1>
# <con1, S, granted>, <con2, S REC_NOT_GAP, granted>, <con3, X, waiting for con1>, <con1, INSERT_INTENTION, waiting for con3>
# <con1, S, granted>, <con3, X, waiting for con1>, <con1, INSERT_INTENTION, waiting for con3>
# Expected: a deadlock, as INSERT INTENTION should not overtake locks on gap, to not slice them
connection con1;
BEGIN;
SELECT * FROM t1 LOCK IN SHARE MODE;
id
1
connection con2;
BEGIN;
SELECT * FROM t1 WHERE id=1 LOCK IN SHARE MODE;
id
1
connection con3;
SET DEBUG_SYNC = 'lock_wait_before_suspend SIGNAL con3_will_wait';
SELECT * FROM t1 FOR UPDATE;
connection con1;
SET DEBUG_SYNC = 'now WAIT_FOR con3_will_wait';
SET DEBUG_SYNC = 'lock_wait_start SIGNAL con1_will_wait';
INSERT INTO t1 VALUES (0);
connection con2;
SET DEBUG_SYNC = 'now WAIT_FOR con1_will_wait';
COMMIT;
connection con1;
ROLLBACK;
connection con3;
ERROR 40001: Deadlock found when trying to get lock; try restarting transaction
# More complicated scenario.
# <con1, S, granted>,
# <con1, S, granted>, <con2, S REC_NOT_GAP, granted>,
# <con1, S, granted>, <con2, S REC_NOT_GAP, granted>, <con3, X, waiting for con1>
# <con1, S, granted>, <con2, S REC_NOT_GAP, granted>, <con3, X, waiting for con1>, <con1, X REC_NOT_GAP, waiting for con2>
# Before MDEV-34877:
# <con1, S, granted>, <con3, X, waiting for con1>, <con1, X REC_NOT_GAP, waiting for con3>
# After MDEV-34877:
# <con1, S, granted>, <con1, X REC_NOT_GAP, granted>, <con3, X, waiting for con1>
connection con1;
BEGIN;
SELECT * FROM t1 LOCK IN SHARE MODE;
id
1
connection con2;
BEGIN;
SELECT * FROM t1 WHERE id=1 LOCK IN SHARE MODE;
id
1
connection default;
connection con3;
SET DEBUG_SYNC = 'lock_wait_before_suspend SIGNAL con3_will_wait';
SELECT * FROM t1 FOR UPDATE;
connection con1;
SET DEBUG_SYNC = 'now WAIT_FOR con3_will_wait';
SET DEBUG_SYNC = 'lock_wait_before_suspend SIGNAL con1_will_wait';
SELECT * FROM t1 WHERE id=1 FOR UPDATE;
connection con2;
SET DEBUG_SYNC = 'now WAIT_FOR con1_will_wait';
COMMIT;
connection con1;
id
1
COMMIT;
connection con3;
id
1
COMMIT;
# A secenario, where con1 has to bypass two transactions:
# <con1, S, granted>
# <con1, S, granted> <con2, X, waiting>
# <con1, S, granted> <con2, X, waiting> <con3, X, waiting>
# Before MDEV-34877:
# <con1, S, granted> <con2, X, waiting> <con3, X, waiting> <con1, X REC_NOT_GAP, waiting for con2>
# After MDEV-34877:
# <con1, S, granted> <con1, X REC_NOT_GAP, granted> <con2, X, waiting> <con3, X, waiting>
connection con1;
BEGIN;
SELECT * FROM t1 LOCK IN SHARE MODE;
id
1
connection con2;
SET DEBUG_SYNC = 'lock_wait_before_suspend SIGNAL con2_will_wait';
SELECT * FROM t1 FOR UPDATE;
connection con3;
SET DEBUG_SYNC = 'now WAIT_FOR con2_will_wait';
SET DEBUG_SYNC = 'lock_wait_before_suspend SIGNAL con3_will_wait';
SELECT * FROM t1 FOR UPDATE;
connection con1;
SET DEBUG_SYNC = 'now WAIT_FOR con3_will_wait';
SELECT * FROM t1 WHERE id=1 FOR UPDATE;
id
1
COMMIT;
connection con2;
id
1
COMMIT;
connection con3;
id
1
COMMIT;
connection default;
disconnect con1;
disconnect con2;
disconnect con3;
disconnect stop_purge;
DROP TABLE t1;
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