To avoid placing a large number of locks that might impact the execution of other concurrent transactions, it is recommended that you avoid running transactions at isolation level 3.
When the nature of an operation demands that it run at isolation level 3, you can lower its impact on concurrency by designing the query to read as few rows and index entries as possible. These steps will help the level 3 transaction run more quickly and, of possibly greater importance, will reduce the number of locks it places.
When at least one operation executes at isolation level 3, you may find that adding an index improves transaction speed. An index can have two benefits:
An index enables rows to be located in an efficient manner
Searches that make use of the index may need fewer locks.
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