Repeatable reads:- Repeatable reads condition occur when a transaction tries to read a data multiple times and and between the two reads, another transaction modified that data. In Lost update, a successfully updated value of a data written in the database is overrides accidentally by the some another transaction updating the same data concurrently.
READ COMMITTED ISOLATION LEVEL SQL SERVER 2012 UPDATE
Lost updates:- It happen when more than one transaction tries to update the same data. There is a risk, that this other transaction may never be committed, leaving the original transaction with wrong data. If higher levels of Isolation is set then it eliminate the concurrency related problem but it results in less number of concurrent access and it may result in data blockingĭirty reads:- This situation happens when a transaction tries to read a data by some other concurrent transaction which is not committed yet. If low level of Isolation is set, it allows multiple users to access the resources concurrently but it may result in many concurrency related problems like phantom reads, dirty reads etc. This is achieved with the help of locks but what locks are needed and how they can be established is decided on the isolation level set on the database level.
Isolation levels :- Isolation level is required to isolate a resource and protect it from other transactions.
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