SQL Server Locks

Lock Contention Solved

If you used Streamload.com at all during June, July, and August, you probably got a "You were the deadlock loser" error, or a "Lock timeout" error, or an "Object required" error. These were all caused by lock contention. After scouring the documentation and talking to a few people, I learned what I summarized above and will say again here:

  • SQL Server starts with row-level locks, but often escalates these to page and table locks, causing deadlocks
  • SQL Server requires locks for reading from the database (SELECTs), so even folks not trying to modify the database are affected by the lock system.

Fortunately, I stumbled across some obscure keywords from the SQL Server lexicon: NOLOCK and ROWLOCK. They are used like this:

WHERE Username LIKE 'foobar'


SET Username = 'fred' WHERE Username = 'foobar'

What do these extra incantations do? We'll examine these two hints - NOLOCK and ROWLOCK - on the next page!

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