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(captured from a very good?Hibernate Book,?copyright belongs to the author)

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First type lost

First transaction’s rollback overwrite second transaction’s update on same record

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Second type lost

First transaction’s commit overwrite second transaction’s update on the same record

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Dirty Read

Read uncommitted data

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Phantom Read

Second read get extra record

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Non-repeatable read

Two read return’s different result.

?(All above issues is due to someone did something in the middle of a transaction, I hate being interupted)

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If one session has exception, need close it, not resue again.

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Database Lock types

share

exclusive

update

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Database lock applied ranges

1. database

2. table

3. area

5. page

6. record

...

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?Transaction optimize

1. short transaction

2. reduce the transaction isolation level if consistency is not strict

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Database Lock

1. Optimistic lock

• Version field goes after the definition of ID
• timestamp can also do the job
• version is better than timestamp, because system only check to second, actually transaction might happen within 1 second.

2. Pessmistic lock

• application lock through database exclusive lock
• database add extra column as locker

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Hibernate transaction