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MySQL re-orders commits
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Schema | |
========================================== | |
CREATE TABLE locks ( | |
name VARCHAR(191) PRIMARY KEY, | |
clock BIGINT | |
); | |
CREATE TABLE ledger ( | |
seq BIGINT AUTO_INCREMENT PRIMARY KEY, | |
entry MEDIUMTEXT | |
); | |
Session A | Session B | |
========================================================|==================================================== | |
BEGIN | BEGIN | |
UPDATE locks SET clock=clock+1 WHERE name='ledger' | | |
| UPDATE locks SET clock=clock+1 WHERE name='ledger' | |
INSERT INTO ledger (entry) VALUES('a') | | |
INSERT INTO ledger (entry) VALUES('b') | | |
INSERT INTO ledger (entry) VALUES('c') | | |
INSERT INTO ledger (entry) VALUES('d') | | |
COMMIT | | |
| INSERT INTO ledger (entry) VALUES('e') | |
| COMMIT | |
============================================================================================================= | |
Clients briefly see rows inserted by Session B before Session A: | |
SELECT * FROM ledger WHERE seq > 0 | |
--------------------- | |
| seq | entry | | |
--------------------- | |
| 5 | e | | |
--------------------- |
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