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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.
72 lines
2.7 KiB
Text
72 lines
2.7 KiB
Text
--source include/have_innodb.inc
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--source include/have_debug.inc
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--source include/have_debug_sync.inc
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--source include/count_sessions.inc
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--connect (pause_purge,localhost,root)
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START TRANSACTION WITH CONSISTENT SNAPSHOT;
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--connection default
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CREATE TABLE t (pk int PRIMARY KEY, sk INT UNIQUE) ENGINE=InnoDB;
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INSERT INTO t VALUES (10, 100);
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--connect (con1,localhost,root)
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BEGIN; # trx 0
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SELECT * FROM t WHERE sk = 100 FOR UPDATE;
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--connect (con2,localhost,root)
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SET DEBUG_SYNC="lock_wait_suspend_thread_enter SIGNAL insert_wait_started";
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# trx 1 is locked on try to read the record in secondary index during duplicates
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# check. It's the first in waiting queue, that's why it will be woken up firstly
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# when trx 0 commits.
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--send INSERT INTO t VALUES (5, 100) # trx 1
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--connect (con3,localhost,root)
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# MDEV-30225 is fixed only for RR
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SET TRANSACTION ISOLATION LEVEL REPEATABLE READ;
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SET DEBUG_SYNC="now WAIT_FOR insert_wait_started";
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SET DEBUG_SYNC="lock_wait_suspend_thread_enter SIGNAL delete_started_waiting";
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# trx 2 can delete (5, 100) on master, but not on slave, as on slave trx 1
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# can insert (5, 100) after trx 2 positioned it's cursor. Trx 2 lock is placed
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# in waiting queue after trx 1 lock, but its persistent cursor position was
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# stored on (100, 10) record in secondary index before suspending. After trx 1
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# is committed, trx 2 will restore persistent cursor position on (100, 10). As
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# (100, 5) secondary index record was inserted before (100, 10) in logical
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# order, and (100, 10) record is delete-marked, trx 2 just continues scanning.
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#
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# Note. There can be several records with the same key in unique secondary
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# index, but only one of them must be non-delete-marked. That's why when we do
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# point query, cursor position is set in the first record in logical order, and
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# then records are iterated until either non-delete-marked record is found or
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# all records with the same unique fields are iterated.
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--send DELETE FROM t WHERE sk = 100 # trx 2
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--connection con1
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SET DEBUG_SYNC="now WAIT_FOR delete_started_waiting";
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DELETE FROM t WHERE sk=100; # trx 0
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COMMIT;
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--disconnect con1
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--connection con2
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--reap
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--disconnect con2
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--connection con3
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# If the bug is fixed, deadlock error will be there, as trx 2 owns
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# next-key lock waiting for trx 1, and trx 1 requests
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# insert-intention lock, conflicting with trx 2 next-key lock.
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--error ER_LOCK_DEADLOCK
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--reap
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--disconnect con3
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--connection default
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# If the bug is not fixed, we will see the row inserted by trx 1 here. This can
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# cause duplicate key error on slave, when some other trx tries in insert row
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# with the same secondary key, as was inserted by trx 1, and not deleted by trx
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# 2.
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SELECT * FROM t;
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--disconnect pause_purge
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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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