Hash Warnings | Clipmarks


	Hash Warnings

Osolage

4-10-2007 4:33 PM

322 views

tags:

sql server, performance, tuning, database

Osolage says:

Yep, this is definitely something I should take a look at then.

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<div style="margin: 12px 0px; font-family: arial; color: #333333; background: #ffffff; border: solid 4px #e5e5e5; width: 100%; clear: left;"><div class="CM_CTB_Content_Wrap" style="margin: 0px; padding: 0px;background-color: #ffffff;"><div style="border-bottom: solid 1px #dcdcdc; white-space: nowrap; margin-bottom: 8px; background-color: #eeeeee ;background-image: url(http://clipmarks.com/images/source-bg.gif); background-repeat: repeat-x; height: 24px; line-height: 24px; vertical-align: middle; padding-bottom: 4px; color: #666666; font-size: 10px;" ><a href="http://clipmarks.com/clip-to-blog/" title="see clips that are hot right now"><img src="http://content.clipmarks.com/blog_embed/4359ccdf-6d34-404b-8064-7f7f0808bbbd/6AE84865-6D3E-42B0-BCE7-42C63D7C2CFD/" alt="" width="19" height="19" border="0" style="vertical-align: middle; margin: 0px 4px; display: inline; border: none; float:none;" /></a>clipped from <a title="http://www.sql-server-performance.com/sql_server_profiler_tips.asp" href="http://www.sql-server-performance.com/sql_server_profiler_tips.asp" style="font-size: 11px;">www.sql-server-performance.com</a></div><blockquote style="text-align: left; padding: 0px 8px; margin: 4px 0px 8px 0px; background: transparent; border: none;" cite="http://www.sql-server-performance.com/sql_server_profiler_tips.asp"><STRONG>Hash Warning</STRONG>: This event is used to measure hash recursions or hash bails that have occurred on your server. A <EM>hash recursion</EM> (event 0) happens when the input of the query does not fit entirely into memory, forcing SQL Server to split the input into multiple parts, which are then processed individually. A <EM>hash bail</EM> (event 1) is even worse for performance. It occurs when a hashing operation reaches its maximum recursion depth, which forces the query to run under an alternative query plan, one that is much less than optimal. Think of a hash bail as a hash recursion's worst nightmare. As you can imagine, these two events can really slow down a query. Some options to correct these problem events include: insure that the Index Statistics are up-to-date for any relevant indexes, rewrite the query, experiment with optimizer hints, or add more RAM to the server.</blockquote></div><div style="margin: 0px 6px 6px 4px;"><table style="font-size: 11px;border-spacing: 0px;padding: 0px;" cellpadding="0" cellspacing="0" width="100%"><tr><td style="background:transparent;border-width:0px;padding:0px;">&nbsp;</td><td align="right" style="background:transparent;border-width:0px;padding:0px;width:107px" width="107"><a href="http://clipmarks.com/share/6AE84865-6D3E-42B0-BCE7-42C63D7C2CFD/blog/" title="blog or email this clip"><img src="http://content6.clipmarks.com/images/c2b-foot.png" border="0" alt="blog it" width="107" height="17" style="border-width:0px;padding:0px;margin:0px;" /></a></td></tr></table></div></div>

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