Why better isolation level means better performance in MS SQL Server
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by Oleg Zhylin
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Published on 2010-03-15T22:04:58Z
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2010/03/15
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When measuring performance on my query I came up with a dependency between isolation level and elapsed time that was surprising to me
READUNCOMMITTED - 409024
READCOMMITTED - 368021
REPEATABLEREAD - 358019
SERIALIZABLE - 348019
Left column is table hint, and the right column is elapsed time in microseconds (sys.dm_exec_query_stats.total_elapsed_time). Why better isolation level gives better performance? This is a development machine and no concurrency whatsoever happens. I would expect READUNCOMMITTED to be the fasted due to less locking overhead.
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