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POQuestion about SQL Server HierarchyID depth-first performance
 

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  1. POQuestion about SQL Server HierarchyID depth-first performance
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    <p>I am trying to implement hierarchyID in a table (dbo.[Message]) containing roughly 50,000 rows (will grow substantially in the future). However it takes 30-40 seconds to retrieve about 25 results.</p> <p>The root node is a filler in order to provide uniqueness, therefor every subsequent row is a child of that dummy row. </p> <p>I need to be able to traverse the table depth-first and have made the hierarchyID column (dbo.[Message].MessageID) the clustering primary key, have also added a computed smallint (dbo.[Message].Hierarchy) which stores the level of the node.</p> <p>Usage: A .Net application passes through a hierarchyID value into the database and I want to be able to retrieve all (if any) children AND parents of that node (besides the root, as it is filler).</p> <p>A simplified version of the query I am using:</p> <pre><code>@MessageID hierarchyID /* passed in from application */ SELECT m.MessageID, m.MessageComment FROM dbo.[Message] as m WHERE m.Messageid.IsDescendantOf(@MessageID.GetAncestor((@MessageID.GetLevel()-1))) = 1 ORDER BY m.MessageID </code></pre> <p>From what I understand, the index should be detected automatically without a hint.</p> <p>From searching forums I have seen people utilizing index hints when dealing with breadth-first indexes, but have not observed this application in depth-first situations. Would that be a relevant approach for my scenario?</p> <p>I have spent the past few days trying to find a solution for this issue, but to no avail. I would greatly appreciate any assistance, and as this is my first post, I apologize in advance if this would be considered a 'noobish' question, I have read the MS documentation and searched countless forums, but have not came across a succinct description of the specific issue. </p>
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    1. COBy the way, the query that you have? As written, it's always going select ALL nodes in the entire table. The `@MessageID.GetAncestor(@MessageID.GetLevel() - 1)` takes it all the way up to the root, and then you select everything that's a descendant, which is... everything. That's why it's so slow.
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    2. COJust to clarify: my situation necessitates the use of depth-first indexing, sorry for confusion (i was referring to breadth-first at the end simply to provide an example of where people have suggested using index-hints)
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