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What is a NOLOCK?
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Answer / michael
Advantage:
applying nolock in select statement will increase
concurreny and performance in fetching.
Disadvantage:
it does'nt consider the transaction scenario, even if the
transaction is under process not yet commited or rollback
it will fetch the current record
eg
begin tran
insert into tablename
values('1','asdf')
select * from tablename with (nolock)
-- it will display the table with inserted record.
but the transaction is not completed, it can be rollback
so it became dirty read.
| Is This Answer Correct ? | 28 Yes | 2 No |
Answer / naren
Using NOLOCK politely asks SQL Server to ignore locks and
read directly from the tables. This means you completely
circumvent the lock system, which is a major performance
and scalability improvement. However, you also completely
circumvent the lock system, which means your code is living
dangerously. You might read the not-necessarily-valid
uncommitted modifications of a running transaction. This is
a calculated risk.
| Is This Answer Correct ? | 19 Yes | 1 No |
Answer / guest
Do not issue shared locks and do not honor exclusive locks.
When this option is in effect, it is possible to read an
uncommitted transaction or a set of pages that are rolled
back in the middle of a read. Dirty reads are possible. Only
applies to the SELECT statement.
| Is This Answer Correct ? | 16 Yes | 3 No |
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