?
(captured from a very good?Hibernate Book,?copyright belongs to the author)
?
First type lost
First transaction’s rollback overwrite second transaction’s update on same record
?
Second type lost
First transaction’s commit overwrite second transaction’s update on the same record
?
Dirty Read
Read uncommitted data
?
Phantom Read
Second read get extra record
?
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)
?
If one session has exception, need close it, not resue again.
??
Database Lock types
share
exclusive
update
?
Database lock applied ranges
1. database
2. table
3. area
5. page
6. record
...
?
?Transaction optimize
1. short transaction
2. reduce the transaction isolation level if consistency is not strict
?
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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