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POSQL Server full text query across multiple tables - why so slow?
 

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  1. POSQL Server full text query across multiple tables - why so slow?
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    <p>I'm trying to understand the performance of an SQL Server 2008 full-text query I am constructing.</p> <p>The following query, using a full-text index, returns the correct results immediately:</p> <pre><code>SELECT O.ID, O.Name FROM dbo.EventOccurrence O WHERE FREETEXT(O.Name, 'query') </code></pre> <p>ie, all EventOccurrences with the word 'query' in their name. And the following query, using a full-text index from a different table, also returns straight away:</p> <pre><code>SELECT V.ID, V.Name FROM dbo.Venue V WHERE FREETEXT(V.Name, 'query') </code></pre> <p>ie. all Venues with the word 'query' in their name. But if I try to join the tables and do both full-text queries at once, it 12 seconds to return:</p> <pre><code>SELECT O.ID, O.Name FROM dbo.EventOccurrence O INNER JOIN dbo.Event E ON O.EventID = E.ID INNER JOIN dbo.Venue V ON E.VenueID = V.ID WHERE FREETEXT(E.Name, 'search') OR FREETEXT(V.Name, 'search') </code></pre> <p>Here is the execution plan: <a href="http://uploadpad.com/files/query.PNG" rel="noreferrer">http://uploadpad.com/files/query.PNG</a></p> <p><strong>UPDATE: the plan in in text form:</strong></p> <pre><code> |--Nested Loops(Left Semi Join, OUTER REFERENCES:([E].[ID], [V].[ID])) |--Hash Match(Inner Join, HASH:([E].[ID])=([O].[EventID])) | |--Hash Match(Inner Join, HASH:([V].[ID])=([E].[VenueID])) | | |--Clustered Index Scan(OBJECT:([iScene].[dbo].[Venue].[PK_Venue] AS [V])) | | |--Clustered Index Scan(OBJECT:([iScene].[dbo].[Event].[PK_Event] AS [E])) | |--Clustered Index Scan(OBJECT:([iScene].[dbo].[EventOccurrence].[PK_EventOccurrence] AS [O])) |--Concatenation |--Table-valued function |--Table-valued function </code></pre> <p>From my reading, I didn't think it was even possible to make a free text query across multiple tables in this way, so I'm not sure I am understanding this correctly.</p> <p>Note that if I remove the WHERE clause from this last query then it returns all results within a second, so it's definitely the full-text that is causing the issue here.</p> <p>Can someone explain (i) why this is so slow and (ii) if this is even supported / if I am even understanding this correctly.</p> <p>Thanks in advance for your help.</p>
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    1. USMike Chamberlain
    1. USMike Chamberlain
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      1. USIbrahim Abdulkarim
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    1. COCan you post the actual plan. Not the picture?
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      1. USMartin Smith
    2. COOK just added it for you.
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      1. USMike Chamberlain
 

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