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4e1e9ea6f3
From the very beginning, the default InnoDB transaction isolation level
REPEATABLE READ does not correspond to any well formed definition.
The main issue is the lack of write/write conflict detection.
To fix that and to make REPEATABLE READ correspond to Snapshot Isolation,
b8a6719889 introduced the Boolean
session variable innodb_snapshot_isolation. It was disabled by default
in order not to break any user applications.
In a new major version of MariaDB Server, we had better enable this
parameter by default.
34 lines
1.2 KiB
Text
34 lines
1.2 KiB
Text
CREATE TABLE t (a int PRIMARY KEY, b int) engine = InnoDB STATS_PERSISTENT=0;
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CREATE TABLE t2 (a int PRIMARY KEY) engine = InnoDB STATS_PERSISTENT=0;
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INSERT INTO t VALUES (10, 10), (20, 20), (30, 30);
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INSERT INTO t2 VALUES (10), (20), (30);
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BEGIN;
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UPDATE t2 SET a = a + 100;
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SELECT * FROM t WHERE a = 20 FOR UPDATE;
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a b
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20 20
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connect con_2,localhost,root,,;
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SET innodb_snapshot_isolation=OFF;
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SET TRANSACTION ISOLATION LEVEL READ COMMITTED;
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SET DEBUG_SYNC = 'lock_trx_handle_wait_enter SIGNAL upd_locked WAIT_FOR upd_cont';
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SET DEBUG_SYNC = 'trx_t_release_locks_enter SIGNAL sel_cont WAIT_FOR upd_cont_2';
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BEGIN;
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UPDATE t SET b = 100;
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connection default;
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SET DEBUG_SYNC="now WAIT_FOR upd_locked";
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SET DEBUG_SYNC="deadlock_report_before_lock_releasing SIGNAL upd_cont WAIT_FOR sel_cont";
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SET DEBUG_SYNC="lock_wait_before_suspend SIGNAL sel_before_suspend";
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SELECT * FROM t WHERE a = 10 FOR UPDATE;;
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connect con_3,localhost,root,,;
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SET DEBUG_SYNC="now WAIT_FOR sel_before_suspend";
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SET DEBUG_SYNC="now SIGNAL upd_cont_2";
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disconnect con_3;
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connection con_2;
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ERROR 40001: Deadlock found when trying to get lock; try restarting transaction
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disconnect con_2;
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connection default;
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a b
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10 10
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SET DEBUG_SYNC = 'RESET';
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DROP TABLE t;
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DROP TABLE t2;
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