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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.
37 lines
1.4 KiB
Plaintext
37 lines
1.4 KiB
Plaintext
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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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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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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INSERT INTO t VALUES(10, 20);
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connect con_del_2,localhost,root,,;
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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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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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connection default;
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disconnect prevent_purge;
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InnoDB 0 transactions not purged
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SET DEBUG_SYNC = 'now SIGNAL first_ins_cont';
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connection con_del_2;
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connection con_ins_1;
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connection default;
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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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