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I saw some contradictions in most of the SQL Server books out there…

But today I saw this and it was too much… Please let me know if I am missing something/crazy.

In Kalen Delaney’s chapter on concurrency she says:

"With pessimistic concurrency, the default behavior is for SQL Server to acquire locks to block access to data that another process is using"

So with pessimistic we acquire locks…

"Pessimistic concurrency avoids conflicts by acquiring locks on data that’s being read, so no other processes can modify that data"

ok… she even tries to be crystal clear by saying:

"readers block writers"

A few lines later, she explains “read uncommitted”, and she goes like…

"Read Uncommitted isolation is implemented by allowing your read operations to not take any locks"

"Read Uncommitted isolation is a pessimistic solution to the problem" ?! what? really?! Please tell me he meant “read uncommitted is an optimistic solution”

Chicago1988
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  • There are two optimistic isolation levels in SQL Server - read committed snapshot isolation and snapshot isolation. Everything else is pessimistic, in sense that optimistic is realized using row versioning, and pessimistic not. – dean Sep 21 '16 at 15:27
  • I think this article explains it very clear : https://www.brentozar.com/archive/2013/01/implementing-snapshot-or-read-committed-snapshot-isolation-in-sql-server-a-guide/ – GuidoG Sep 21 '16 at 15:35

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