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hemantdangi-gchemantdangi-gc
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MDEV-25039: MDL BF-BF conflict because of foreign key
Issue: The Commit: 0584846 'Add TL_FIRST_WRITE in SQL layer for determining R/W' limits INSERT statements on write nodes to acquire MDL locks on it's all child tables and thereby wsrep certification keys added, but on applier nodes it does acquire MDL locks for all child tables. This can result into MDL BF-BF conflict on applier node when transactions referring to parent and child tables are executed concurrently. For example: Tables with foreign keys: t1<-t2<-t3<-t4 Conflicting transactions: INSERT t1 and DROP TABLE t4 Wsrep certification keys taken on write node: - for INSERT t1: t1 and t2 - for DROP TABLE t4: t4 On applier node MDL BF-BF conflict happened between two transaction because MDL locks on t1, t2, t3 and t4 were taken for INSERT t1, which conflicted with MDL lock on t4 taken by DROP TABLE t4. The Wsrep certification keys helps in resolving this MDL BF-BF conflict by prioritizing and scheduling concurrent transactions. But to generate Wsrep certification keys it needs to open and take MDL locks on all the child tables. The Commit: 0584846 change limits MDL lock to be taken on all child nodes for read-only FK checks (INSERT t1). But this doesn't works on applier nodes because Write_rows_log_event event logged for INSERT is also used to record update (check Write_rows_log_event::get_trg_event_map()), and therefore MDL locks is taken for all the child tables on applier node for update and insert event. Solution: Additional keys for the referenced/foreign table needs to be added to avoid potential MDL conflicts with concurrent update and DDLs.
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‎mysql-test/suite/galera/r/galera_multi_level_fk_ddl_insert.result‎

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connection node_2;
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connection node_1;
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#
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# 1. BF-BF conflict on MDL locks between: DROP TABLE t4 and INSERT t1
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# with foreign key references as below:
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# - t1<-t2<-t3<-t4
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#
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connection node_2;
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SET GLOBAL wsrep_slave_threads=2;
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CREATE TABLE t1 (
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id INTEGER PRIMARY KEY,
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f2 INTEGER
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);
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CREATE TABLE t2 (
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id INT PRIMARY KEY,
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t1_id INT NOT NULL,
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f2 INTEGER NOT NULL,
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KEY key_t1_id(t1_id),
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CONSTRAINT key_t1_id FOREIGN KEY (t1_id) REFERENCES t1 (id) ON UPDATE CASCADE ON DELETE CASCADE
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);
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CREATE TABLE t3 (
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id INT PRIMARY KEY,
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t2_id INT NOT NULL,
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f2 INTEGER NOT NULL,
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KEY key_t2_id(t2_id),
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CONSTRAINT key_t2_id FOREIGN KEY (t2_id) REFERENCES t2 (id) ON UPDATE CASCADE ON DELETE CASCADE
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);
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CREATE TABLE t4 (
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id INT PRIMARY KEY,
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t3_id INT NOT NULL,
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f2 INTEGER NOT NULL,
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KEY key_t3_id(t3_id),
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CONSTRAINT key_t3_id FOREIGN KEY (t3_id) REFERENCES t3 (id) ON UPDATE CASCADE ON DELETE CASCADE
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);
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INSERT INTO t1 VALUES (1,0);
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INSERT INTO t1 VALUES (2,0);
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INSERT INTO t2 VALUES (1,1,1234);
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INSERT INTO t2 VALUES (2,2,1234);
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INSERT INTO t3 VALUES (1,1,1234);
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INSERT INTO t3 VALUES (2,2,1234);
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INSERT INTO t4 VALUES (1,1,1234);
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INSERT INTO t4 VALUES (2,2,1234);
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connection node_2;
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SET GLOBAL DEBUG_DBUG = '+d,sync.wsrep_apply_toi';
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connection node_1;
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DROP TABLE t4;
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connection node_2;
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SET DEBUG_SYNC = "now WAIT_FOR sync.wsrep_apply_toi_reached";
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SET SESSION wsrep_sync_wait = 0;
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connection node_1;
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SET GLOBAL DEBUG_DBUG = '+d,wsrep_print_foreign_keys_table';
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START TRANSACTION;
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INSERT INTO t1 VALUES (3,0);
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COMMIT;
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connection node_2;
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SET GLOBAL DEBUG_DBUG = '-d,sync.wsrep_apply_toi';
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SET DEBUG_SYNC = "now SIGNAL signal.wsrep_apply_toi";
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SET DEBUG_SYNC = 'RESET';
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SET GLOBAL DEBUG_DBUG = "";
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SET GLOBAL wsrep_slave_threads=DEFAULT;
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connection node_1;
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SET DEBUG_SYNC = 'RESET';
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SET GLOBAL DEBUG_DBUG = "";
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SET GLOBAL wsrep_slave_threads=DEFAULT;
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connection node_1;
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include/assert_grep.inc [Foreign key referenced table found: 2 tables]
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include/assert_grep.inc [Foreign key referenced table found: test.t2]
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include/assert_grep.inc [Foreign key referenced table found: test.t3]
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connection node_2;
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select * from t1;
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id f2
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1 0
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2 0
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3 0
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select * from t2;
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id t1_id f2
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1 1 1234
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2 2 1234
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select * from t3;
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id t2_id f2
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1 1 1234
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2 2 1234
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select * from t4;
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ERROR 42S02: Table 'test.t4' doesn't exist
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connection node_1;
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select * from t1;
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id f2
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1 0
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2 0
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3 0
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select * from t2;
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id t1_id f2
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1 1 1234
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2 2 1234
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select * from t3;
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id t2_id f2
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1 1 1234
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2 2 1234
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select * from t4;
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ERROR 42S02: Table 'test.t4' doesn't exist
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DROP TABLE t3, t2, t1;
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#
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# 2. BF-BF conflict on MDL locks between:
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# ALTER TABLE t4 (whose parent table are t4 -> t3 -> t2 -> t1), and
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# INSERT on t1.
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#
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connection node_2;
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SET GLOBAL wsrep_slave_threads=2;
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CREATE TABLE t1 (
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id INTEGER PRIMARY KEY,
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f2 INTEGER
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);
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CREATE TABLE t2 (
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id INT PRIMARY KEY,
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t1_id INT NOT NULL,
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f2 INTEGER NOT NULL,
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KEY key_t1_id(t1_id),
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CONSTRAINT key_t1_id FOREIGN KEY (t1_id) REFERENCES t1 (id) ON UPDATE CASCADE ON DELETE CASCADE
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);
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CREATE TABLE t3 (
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id INT PRIMARY KEY,
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t2_id INT NOT NULL,
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f2 INTEGER NOT NULL,
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KEY key_t2_id(t2_id),
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CONSTRAINT key_t2_id FOREIGN KEY (t2_id) REFERENCES t2 (id) ON UPDATE CASCADE ON DELETE CASCADE
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);
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CREATE TABLE t4 (
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id INT PRIMARY KEY,
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t3_id INT NOT NULL,
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f2 INTEGER NOT NULL,
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KEY key_t3_id(t3_id)
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);
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INSERT INTO t1 VALUES (1,0);
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INSERT INTO t1 VALUES (2,0);
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INSERT INTO t2 VALUES (1,1,1234);
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INSERT INTO t2 VALUES (2,2,1234);
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INSERT INTO t3 VALUES (1,1,1234);
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INSERT INTO t3 VALUES (2,2,1234);
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INSERT INTO t4 VALUES (1,1,1234);
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INSERT INTO t4 VALUES (2,2,1234);
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connection node_2;
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SET GLOBAL DEBUG_DBUG = '+d,sync.wsrep_apply_toi';
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connection node_1;
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ALTER TABLE t4 ADD CONSTRAINT key_t3_id FOREIGN KEY (t3_id) REFERENCES t3 (id) ON UPDATE CASCADE ON DELETE CASCADE;
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connection node_2;
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SET DEBUG_SYNC = "now WAIT_FOR sync.wsrep_apply_toi_reached";
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SET SESSION wsrep_sync_wait = 0;
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connection node_1;
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SET GLOBAL DEBUG_DBUG = '+d,wsrep_print_foreign_keys_table';
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START TRANSACTION;
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INSERT INTO t1 VALUES (3,0);
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COMMIT;
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connection node_2;
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SET GLOBAL DEBUG_DBUG = '-d,sync.wsrep_apply_toi';
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SET DEBUG_SYNC = "now SIGNAL signal.wsrep_apply_toi";
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SET DEBUG_SYNC = 'RESET';
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SET GLOBAL DEBUG_DBUG = "";
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SET GLOBAL wsrep_slave_threads=DEFAULT;
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connection node_1;
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SET DEBUG_SYNC = 'RESET';
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SET GLOBAL DEBUG_DBUG = "";
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SET GLOBAL wsrep_slave_threads=DEFAULT;
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connection node_1;
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include/assert_grep.inc [Foreign key referenced table found: 3 tables]
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include/assert_grep.inc [Foreign key referenced table found: test.t2]
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include/assert_grep.inc [Foreign key referenced table found: test.t3]
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include/assert_grep.inc [Foreign key referenced table found: test.t4]
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connection node_2;
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select * from t1;
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id f2
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1 0
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2 0
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3 0
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select * from t2;
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id t1_id f2
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1 1 1234
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2 2 1234
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select * from t3;
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id t2_id f2
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1 1 1234
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2 2 1234
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connection node_1;
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select * from t1;
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id f2
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1 0
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2 0
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3 0
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select * from t2;
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id t1_id f2
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1 1 1234
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2 2 1234
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select * from t3;
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id t2_id f2
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1 1 1234
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2 2 1234
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DROP TABLE t4, t3, t2, t1;
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#
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# 3. BF-BF conflict on MDL locks between:
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# CREATE TABLE t3 (whose parent table are t4 -> t3 -> t2 -> t1), and
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# INSERT on t1.
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#
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connection node_2;
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SET GLOBAL wsrep_slave_threads=2;
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CREATE TABLE t1 (
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id INTEGER PRIMARY KEY,
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f2 INTEGER
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);
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CREATE TABLE t2 (
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id INT PRIMARY KEY,
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t1_id INT NOT NULL,
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f2 INTEGER NOT NULL,
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KEY key_t1_id(t1_id),
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CONSTRAINT key_t1_id FOREIGN KEY (t1_id) REFERENCES t1 (id) ON UPDATE CASCADE ON DELETE CASCADE
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);
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CREATE TABLE t3 (
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id INT PRIMARY KEY,
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t2_id INT NOT NULL,
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f2 INTEGER NOT NULL,
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KEY key_t2_id(t2_id),
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CONSTRAINT key_t2_id FOREIGN KEY (t2_id) REFERENCES t2 (id) ON UPDATE CASCADE ON DELETE CASCADE
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);
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INSERT INTO t1 VALUES (1,0);
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INSERT INTO t1 VALUES (2,0);
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INSERT INTO t2 VALUES (1,1,1234);
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INSERT INTO t2 VALUES (2,2,1234);
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INSERT INTO t3 VALUES (1,1,1234);
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INSERT INTO t3 VALUES (2,2,1234);
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connection node_2;
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SET GLOBAL DEBUG_DBUG = '+d,sync.wsrep_apply_toi';
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connection node_1;
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CREATE TABLE t4 (id INT PRIMARY KEY, t3_id INT NOT NULL, f2 INTEGER NOT NULL, KEY key_t3_id(t3_id), CONSTRAINT key_t3_id FOREIGN KEY (t3_id) REFERENCES t3 (id) ON UPDATE CASCADE ON DELETE CASCADE);
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connection node_2;
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SET DEBUG_SYNC = "now WAIT_FOR sync.wsrep_apply_toi_reached";
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SET SESSION wsrep_sync_wait = 0;
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connection node_1;
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SET GLOBAL DEBUG_DBUG = '+d,wsrep_print_foreign_keys_table';
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START TRANSACTION;
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INSERT INTO t1 VALUES (3,0);
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COMMIT;
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connection node_2;
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SET GLOBAL DEBUG_DBUG = '-d,sync.wsrep_apply_toi';
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SET DEBUG_SYNC = "now SIGNAL signal.wsrep_apply_toi";
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SET DEBUG_SYNC = 'RESET';
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SET GLOBAL DEBUG_DBUG = "";
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SET GLOBAL wsrep_slave_threads=DEFAULT;
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connection node_1;
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SET DEBUG_SYNC = 'RESET';
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SET GLOBAL DEBUG_DBUG = "";
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SET GLOBAL wsrep_slave_threads=DEFAULT;
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connection node_1;
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include/assert_grep.inc [Foreign key referenced table found: 2 tables]
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include/assert_grep.inc [Foreign key referenced table found: test.t2]
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include/assert_grep.inc [Foreign key referenced table found: test.t3]
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include/assert_grep.inc [Foreign key referenced table found: test.t4]
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connection node_2;
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select * from t1;
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id f2
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1 0
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2 0
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3 0
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select * from t2;
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id t1_id f2
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1 1 1234
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2 2 1234
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select * from t3;
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id t2_id f2
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1 1 1234
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2 2 1234
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connection node_1;
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select * from t1;
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id f2
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1 0
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2 0
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3 0
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select * from t2;
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id t1_id f2
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1 1 1234
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2 2 1234
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select * from t3;
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id t2_id f2
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1 1 1234
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2 2 1234
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DROP TABLE t4, t3, t2, t1;
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#
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# 4. BF-BF conflict on MDL locks between:
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# OPTIMIZE TABLE t2 (whose parent table are t2 -> t1), and
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# INSERT t1.
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#
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connection node_2;
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SET GLOBAL wsrep_slave_threads=2;
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CREATE TABLE t1 (
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id INTEGER PRIMARY KEY,
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f2 INTEGER
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);
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CREATE TABLE t2 (
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id INT PRIMARY KEY,
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t1_id INT NOT NULL,
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f2 INTEGER NOT NULL,
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KEY key_t1_id(t1_id),
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CONSTRAINT key_t1_id FOREIGN KEY (t1_id) REFERENCES t1 (id) ON UPDATE CASCADE ON DELETE CASCADE
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);
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CREATE TABLE t3 (
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id INT PRIMARY KEY,
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t2_id INT NOT NULL,
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f2 INTEGER NOT NULL,
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KEY key_t2_id(t2_id),
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CONSTRAINT key_t2_id FOREIGN KEY (t2_id) REFERENCES t2 (id) ON UPDATE CASCADE ON DELETE CASCADE
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);
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INSERT INTO t1 VALUES (1,0);
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INSERT INTO t1 VALUES (2,0);
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INSERT INTO t2 VALUES (1,1,1234);
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INSERT INTO t2 VALUES (2,2,1234);
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INSERT INTO t3 VALUES (1,1,1234);
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INSERT INTO t3 VALUES (2,2,1234);
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connection node_2;
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SET GLOBAL DEBUG_DBUG = '+d,sync.wsrep_apply_toi';
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connection node_1;
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OPTIMIZE TABLE t3;
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Table Op Msg_type Msg_text
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test.t3 optimize note Table does not support optimize, doing recreate + analyze instead
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test.t3 optimize status OK
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connection node_2;
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SET DEBUG_SYNC = "now WAIT_FOR sync.wsrep_apply_toi_reached";
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SET SESSION wsrep_sync_wait = 0;
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connection node_1;
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SET GLOBAL DEBUG_DBUG = '+d,wsrep_print_foreign_keys_table';
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START TRANSACTION;
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INSERT INTO t1 VALUES (3,0);
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COMMIT;
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connection node_2;
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SET GLOBAL DEBUG_DBUG = '-d,sync.wsrep_apply_toi';
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SET DEBUG_SYNC = "now SIGNAL signal.wsrep_apply_toi";
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SET DEBUG_SYNC = 'RESET';
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SET GLOBAL DEBUG_DBUG = "";
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SET GLOBAL wsrep_slave_threads=DEFAULT;
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connection node_1;
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SET DEBUG_SYNC = 'RESET';
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SET GLOBAL DEBUG_DBUG = "";
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SET GLOBAL wsrep_slave_threads=DEFAULT;
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connection node_1;
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include/assert_grep.inc [Foreign key referenced table found: 1 tables]
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include/assert_grep.inc [Foreign key referenced table found: test.t2]
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include/assert_grep.inc [Foreign key referenced table found: test.t3]
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connection node_2;
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select * from t1;
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id f2
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1 0
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2 0
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3 0
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select * from t2;
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id t1_id f2
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1 1 1234
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2 2 1234
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connection node_1;
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select * from t1;
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id f2
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1 0
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2 0
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3 0
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select * from t2;
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id t1_id f2
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1 1 1234
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2 2 1234
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DROP TABLE t3, t2, t1;

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