并发事务的ABA问题
arminzheng Lv2
  2022-10-09 00:00:00 2022-10-09 00:00      116 Words  1 Mins  
  • A 事务 (先开启), 此时 num == 0
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BEGIN
SELECT num FROM table_name where log_id ='1'
-- num | 0
-- 等待 事务B 执行
UPDATE table_name set num = num + 1 where log_id = '1'
-- 事务B 提交后, 更新成功结果 由 0 跳到 2
COMMIT;
  • B事物 (后开启)
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BEGIN
SELECT num FROM table_name where log_id ='1'
-- num | 0
UPDATE table_name set num = num + 1 where log_id = '1'
-- num | 1
COMMIT;
  • 不能成功
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BEGIN
SELECT num FROM table_name where log_id ='1'
UPDATE table_name set num = num + 1 where log_id = '1' and num = 0 
COMMIT;
-- affect row 0