f1166c0421
Previously, the view contents could become inconsistent with the base tables in the following scenarios: 1) A concurrent transaction modifies a base table and commits before the incremental view maintenance starts in the current transaction. 2) A concurrent transaction modifies a base table and commits before the create_immv or refresh_immv command generates data. 3) Concurrent transactions incrementally update a view with a self-join or modify multiple base tables simultaneously. Incremental updates of a view are generally performed sequentially using an exclusive lock. However, even if we are able to acquire the lock, a concurrent transaction may have already incrementally updated the view and been committed before we can acquire it. In REPEATABLE READ or SERIALIZABLE isolation levels, this could lead to an inconsistent view state, which is the cause of the first issue. To fix this, a new field, lastivmupdate, has been added to the pg_ivm_immv catalog to record the transaction ID of the most recent update to the view. Before performing view maintenance, the transaction ID is checked. If the transaction was still in progress at the start of the current transaction, an error is raised to prevent anomalies. To fix the second issue, the timing of CreateTrigger() has been moved to before data generation. This ensures that locks conflicting with table modifications have been acquired on all base tables. In addition, the latest snapshot is used in READ COMMITTED level during the data generation to reflect committed changes from concurrent transactions. Additionally, inconsistencies that cannot be avoided through locking are prevented by checking the transaction ID of the last view update, as done for the first issue. However, concurrent table modifications and create_immv execution still cannot be detected at the time of view creation. Therefore, create_immv raises a warning in REPEATABLE READ or SERIALIZABLE isolation levels, suggesting that the command be used in READ COMMITTED mode or that refresh_immv be executed afterward to ensure the view remains consistent. The third issue was caused by the snapshot used for checking tuple visibility in the table's pre-update state not being the latest one. To fix this, the latest snapshot is now used in READ COMMITTED mode. Isolation tests are also added. Issue #104
62 lines
2.2 KiB
Python
62 lines
2.2 KiB
Python
# Test interaction between concurrent transactions performing
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# table modifications in READ COMMITTED isolation level
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setup
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{
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CREATE TABLE a (i int, j int);
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CREATE TABLE b (i int, j int);
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INSERT INTO a VALUES (1,10);
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INSERT INTO b VALUES (1,100);
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SELECT pgivm.create_immv('mv(x,y,z)',
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'SELECT a1.j, a2.j,b.j FROM a AS a1, a AS a2,b WHERE a1.i = a2.i AND a1.i = b.i');
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CREATE VIEW v(x,y,z) AS
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SELECT a1.j, a2.j,b.j FROM a AS a1, a AS a2,b WHERE a1.i = a2.i AND a1.i = b.i;
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CREATE FUNCTION check_mv() RETURNS text AS
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$$ SELECT CASE WHEN count(*) = 0 THEN 'ok' ELSE 'ng' END
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FROM ((SELECT * FROM mv EXCEPT ALL SELECT * FROM v) UNION ALL
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(SELECT * FROM v EXCEPT ALL SELECT * FROM mv)) $$ LANGUAGE sql;
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}
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teardown
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{
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DROP FUNCTION check_mv();
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DROP TABLE mv;
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DROP VIEW v;
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DROP TABLE a;
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DROP TABLE b;
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}
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session tx1
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setup { BEGIN TRANSACTION ISOLATION LEVEL READ COMMITTED; }
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step s1 { SELECT; }
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step insert1 { INSERT INTO a VALUES (2,20); INSERT INTO b VALUES (2,200); }
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step update1 { UPDATE a SET j = 11 WHERE i = 1; }
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step check1 { SELECT check_mv();}
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step c1 { COMMIT; }
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step mv { SELECT * FROM mv ORDER BY 1,2,3; SELECT check_mv(); }
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session tx2
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setup { BEGIN TRANSACTION ISOLATION LEVEL READ COMMITTED; }
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step s2 { SELECT; }
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step insert2 { INSERT INTO a VALUES (1,11), (2,21); INSERT INTO b VALUES (2,201); }
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step update2 { UPDATE b SET j = 111 WHERE i = 1; }
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step check2 { SELECT check_mv(); }
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step c2 { COMMIT; }
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permutation s1 update1 s2 update2 c1 check2 c2 mv
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permutation s1 update1 s2 c1 update2 check2 c2 mv
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permutation s1 s2 update1 update2 c1 check2 c2 mv
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permutation s1 s2 update2 update1 c2 check1 c1 mv
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permutation s1 s2 update1 c1 update2 check2 c2 mv
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permutation s2 update2 s1 update1 c2 check1 c1 mv
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permutation s2 update2 s1 c2 update1 check1 c1 mv
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permutation s2 s1 update2 c2 update1 check1 c1 mv
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permutation s1 insert1 s2 insert2 c1 check2 c2 mv
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permutation s1 insert1 s2 c1 insert2 check2 c2 mv
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permutation s1 s2 insert1 insert2 c1 check2 c2 mv
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permutation s1 s2 insert2 insert1 c2 check1 c1 mv
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permutation s1 s2 insert1 c1 insert2 check2 c2 mv
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permutation s2 insert2 s1 insert1 c2 check1 c1 mv
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permutation s2 insert2 s1 c2 insert1 check1 c1 mv
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permutation s2 s1 insert2 c2 insert1 check1 c1 mv
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