pessimistic

What's the difference between PESSIMISTIC_READ and PESSIMISTIC_WRITE in JPA?

由 最后都变了- 提交于 2020-01-20 13:31:08
问题 I have read the article Locking and Concurrency in Java Persistence 2.0, and run the sample application. But i still cant realize the difference between PESSIMISTIC_READ and PESSIMISTIC_WRITE. I tried to modify the code, and where the code using PESSIMISTIC_READ and PESSIMISTIC_WRITE will have the same result that the sql will invoked with "for update". 回答1: The difference lies in locking mechanism. PESSIMISTIC_READ lock means that dirty reads and non-repeatable reads are impossible when you

What's the difference between PESSIMISTIC_READ and PESSIMISTIC_WRITE in JPA?

由 依然范特西╮ 提交于 2020-01-20 13:30:09
问题 I have read the article Locking and Concurrency in Java Persistence 2.0, and run the sample application. But i still cant realize the difference between PESSIMISTIC_READ and PESSIMISTIC_WRITE. I tried to modify the code, and where the code using PESSIMISTIC_READ and PESSIMISTIC_WRITE will have the same result that the sql will invoked with "for update". 回答1: The difference lies in locking mechanism. PESSIMISTIC_READ lock means that dirty reads and non-repeatable reads are impossible when you

Pessimistic lock in T-SQL

由 故事扮演 提交于 2020-01-10 05:05:33
问题 If i SELECT a row for updating in MS SQL Server, and want to have it locked till i either update or cancel, which option is better :- 1) Use a query hint like UPDLOCK 2) Use REPEATABLE READ isolation level for the transaction 3) any other option. Thanks, Chak. 回答1: Neither. You almost never want to hold a transaction open while your user is inputting data. If you have to implement a pessimistic lock like this, people generally do it by rolling their own functionality. Consider the full

Pessimistic lock in T-SQL

由 我的未来我决定 提交于 2019-11-29 14:43:39
If i SELECT a row for updating in MS SQL Server, and want to have it locked till i either update or cancel, which option is better :- 1) Use a query hint like UPDLOCK 2) Use REPEATABLE READ isolation level for the transaction 3) any other option. Thanks, Chak. Neither. You almost never want to hold a transaction open while your user is inputting data. If you have to implement a pessimistic lock like this, people generally do it by rolling their own functionality. Consider the full ramifications of what you are doing. I once worked on a system that implemented locking like this. You often run
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