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3ddc00dc3b
Before the fix next-key lock was requested only if a record was delete-marked for locking unique search in RR isolation level. There can be several delete-marked records for the same unique key, that's why InnoDB scans the records until eighter non-delete-marked record is reached or all delete-marked records with the same unique key are scanned. For range scan next-key locks are used for RR to protect scanned range from inserting new records by other transactions. And this is the reason of why next-key locks are used for delete-marked records for unique searches. If a record is not delete-marked, the requested lock type was "not-gap". When a record is not delete-marked during lock request by trx 1, and some other transaction holds conflicting lock, trx 1 creates waiting not-gap lock on the record and suspends. During trx 1 suspending the record can be delete-marked. And when the lock is granted on conflicting transaction commit or rollback, its type is still "not-gap". So we have "not-gap" lock on delete-marked record for RR. And this let some other transaction to insert some record with the same unique key when trx 1 is not committed, what can cause isolation level violation. The fix is to set next-key locks for both delete-marked and non-delete-marked records for unique search in RR.
84 lines
3.5 KiB
Plaintext
84 lines
3.5 KiB
Plaintext
--source include/have_innodb.inc
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--source include/count_sessions.inc
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source include/have_debug.inc;
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source include/have_debug_sync.inc;
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CREATE TABLE t (a int PRIMARY KEY, b int NOT NULL UNIQUE) engine = InnoDB;
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--connect(prevent_purge,localhost,root,,)
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start transaction with consistent snapshot;
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--connect(con_del_1,localhost,root,,)
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INSERT INTO t VALUES (20,20);
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SET DEBUG_SYNC = 'innodb_row_search_for_mysql_exit SIGNAL first_del_row_search_mvcc_finished WAIT_FOR first_del_cont';
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--send DELETE FROM t WHERE b = 20
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--connect(con_ins_1,localhost,root,,)
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SET DEBUG_SYNC = 'now WAIT_FOR first_del_row_search_mvcc_finished';
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# It's supposed the following INSERT will be suspended just after
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# lock_wait_suspend_thread_enter syncpoint, and will be awaken
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# after the previous DELETE commits. ib_after_row_insert will be executed
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# after the INSERT is woken up. The previous DELETE will wait for
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# first_del_cont signal before commit, and this signal will be sent later.
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# So it's safe to use two signals in a row here, it's guaranted the first
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# signal will be received before the second signal is sent.
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SET DEBUG_SYNC = 'lock_wait_suspend_thread_enter SIGNAL first_ins_locked';
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SET DEBUG_SYNC = 'ib_after_row_insert SIGNAL first_ins_row_inserted WAIT_FOR first_ins_cont';
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--send INSERT INTO t VALUES(10, 20)
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--connect(con_del_2,localhost,root,,)
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# After MDEV-30225 is fixed, the following DELETE creates next-key lock for
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# unqique search for RR, and the above INSERT kills it as deadlock victim.
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# But it still requests not-gap lock for RC.
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SET TRANSACTION ISOLATION LEVEL READ COMMITTED;
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SET DEBUG_SYNC = 'now WAIT_FOR first_ins_locked';
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SET DEBUG_SYNC = 'lock_wait_suspend_thread_enter SIGNAL second_del_locked';
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###############################################################################
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# This DELETE is locked by the previous DELETE, after that DELETE is
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# committed, it will still be locked by the next INSERT on delete-marked
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# heap_no 2 record. After that INSERT inserted the record with heap_no 3,
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# and after heap_no 2 record is purged, this DELETE will be unlocked and
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# must restore persistent cursor position at heap_no 3 record, as it has the
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# same secondary key value as former heap_no 2 record. Then it must be blocked
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# by the previous INSERT, and after the INSERT is committed, it must
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# delete the record, inserted by the previous INSERT, and the last INSERT(see
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# below) must be finished without error. But instead this DELETE restores
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# persistent cursor position to supremum, as a result, it does not delete the
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# record, inserted by the previous INSERT, and the last INSERT is finished with
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# duplicate key check error.
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###############################################################################
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--send DELETE FROM t WHERE b = 20
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--connection default
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SET DEBUG_SYNC = 'now WAIT_FOR second_del_locked';
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SET DEBUG_SYNC = 'now SIGNAL first_del_cont';
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SET DEBUG_SYNC = 'now WAIT_FOR first_ins_row_inserted';
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--connection con_del_1
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--reap
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--connection default
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--disconnect prevent_purge
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--source include/wait_all_purged.inc
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SET DEBUG_SYNC = 'now SIGNAL first_ins_cont';
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--connection con_del_2
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--reap
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--connection con_ins_1
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--reap
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--connection default
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###############################################################################
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# Duplicate key error is expected if the bug is not fixed.
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###############################################################################
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INSERT INTO t VALUES(30, 20);
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--disconnect con_ins_1
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--disconnect con_del_1
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--disconnect con_del_2
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--connection default
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SET DEBUG_SYNC = 'RESET';
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DROP TABLE t;
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--source include/wait_until_count_sessions.inc
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