NOLOCK in SELECT statement

[HulaGirl]

Does a SELECT query that just read from a set of tables locks these tables while reading? If it does, will a hint NOLOCK improve the performance of the query and hence improve the performance of other queries that read off the same set of tables at the same time?

Does NOLOCK means "don't lock" or "ignore lock"?

Hey, thanks.

 

[bhags]

Nolock Does not issue any shared locks and it do not honor exclusive locks. When this nolock is in effect, it allows to read an uncommitted transaction or a set of pages that are rolled back in the middle of a read.

Muliple select statements can access the same table concurrent if nolock is used, with any performance issues and without locking the table

 

[HulaGirl]

thanks bhags, one more question, does a simple SELECT (read) locks up tables too?