concurrency related problems and control - Isolation levels

concurrency related problems

1-dirty read
2-Nonrepeatable read

3-lost data

4-phantom read

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concurrency control

1-Pessimistic Control.

(SQL Server locks the resource until user performs the action she/he needs and then release for others.)

1/1- Read Uncommitted Isolation Level

1/2- Read Committed Isolation Level

1/3- Repeatable Read Isolation Level

1/4- Serializable Isolation Level

2-Optimistic Control.

(SQL Server does not hold locks but once read, check for inconsistency for next read.)

2/1- Snapshot Isolation Level

2/2- Read Committed Snapshot Isolation Level