Tag: transaction
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Locking and MVCC in MySQL InnoDB 鎖機制與多版本並發控制
Category: Database
最近在研究 MySQL 5.6 / 5.7 InnoDB storage engine 的 Transaction、Locking 和 Multi-Version Concurrency Control (MVCC) 機制，基本上只討論 Isolation level 是 REPEATABLE READ 或 READ COMMITTED 的情況，這一篇是過程中記錄下來的筆記。
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Django's get_or_create() may raise IntegrityError but subsequent get() raises DoesNotExist
Category: Database, Python, Web Development
get_or_create() 拋出 IntegrityError 但是接著 get() 一次卻會是 DoesNotExist，以上的錯誤常常會發生在 MySQL 的 isolation level 是 REPEATABLE READ 的情況下。MySQL 默認採用 REPEATABLE READ（而 PostgreSQL 預設是 READ COMMITTED）。
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Transaction isolation levels in MySQL
Category: Database
A non-repeatable read occurs, when during the course of a transaction, a row is retrieved twice and the values within the row differ between reads.