How does one SELECT block another?

Posted by Krip on Stack Overflow See other posts from Stack Overflow or by Krip
Published on 2010-06-08T17:59:44Z Indexed on 2010/06/08 18:52 UTC
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sql-server

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tsql

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concurrency

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blocking

I'm looking at output of SP_WhoIsActive on SQL Server 2005, and it's telling me one session is blocking another - fine. However they both are running a SELECT. How does one SELECT block another? Shouldn't they both be acquiring shared locks (which are compatible with one another)?

Some more details: Neither session has an open transaction count - so they are stand-alone.

The queries join a view with a table.

They are complex queries which join lots of tables and results in 10,000 or so reads.

Any insight much appreciated.

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