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    <p>A high disk queue length does not mean you have an I/O bottleneck if you have a SAN or NAS, you may want to look at other additional counters. Check out <a href="http://blogs.msdn.com/psssql/archive/2007/02/21/sql-server-urban-legends-discussed.aspx" rel="noreferrer">SQL Server Urban Legends discussed</a> for more details.</p> <p>1: The following operations heavily utilize tempdb</p> <ul> <li>Repeated create and drop of temporary tables (local or global)</li> <li>Table variables that use tempdb for storage purposes</li> <li>Work tables associated with CURSORS</li> <li>Work tables associated with an ORDER BY clause</li> <li>Work tables associated with an GROUP BY clause</li> <li>Work files associated with HASH PLANS</li> </ul> <p>These SQL Server 2005 features also use tempdb heavily:</p> <ul> <li>row level versioning (snapshotisolation) </li> <li>online index re-building</li> </ul> <p>As mentioned in other SO answers read <a href="http://searchsqlserver.techtarget.com/tip/0,289483,sid87_gci1307255,00.html" rel="noreferrer">this article</a> on best practice for increasing tempdb performance. <br> <br> 2: Looking at the amount of free RAM on the server i.e. looking at the WMI counter Memory->Available Mbytes doesn't help as SQL Server will cache data pages in RAM, so any db server that's running long enough will have little free RAM.<br> The counters you should look at that are more meaningful in telling you if adding RAM to the server will help are:<br> <em>SQL Server Instance:Buffer Manager->Page Life Expectancy (in seconds)</em> A value below 300-400 seconds will mean that Pages are not in memory very long and data continually is being read in from disks. Servers that have a low page life expectancy will benefit from additional RAM.<br> and <br> <em>SQL Server Instance:Buffer Manager->Buffer Cache hit Ratio</em> This tells you the percentage of pages that were read from RAM that didn't have to incur a read from disk, a cache hit ratio lower then 85 will mean that the server will benefit from additional RAM <br> <br> 3: Yes, can't go wrong here. Having tempdb on a separate set of disks is recommended. Look at <a href="http://support.microsoft.com/kb/224071" rel="noreferrer">this KB article</a> under the heading: Moving the tempdb database on how to do this.</p>
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    1. COreviewed Page Life Expectancy and Buffer Cache hit Ratio (not sure why i didn't think of this, since I had a memory issue in the past). Page Life expectancy was 74000 and Buffer Cache was 99.85. Pretty sure that means it's not a memory issue!
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    2. COTurns out a single missing index was causing every bit of my problems- i could watch disk queue, disk sec/write, and disk sec/read plummet the second i created the index. The results from a table of 3 million records were being sorted in the tempdb from what i could tell.
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