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Thread: Linked Servers: Pass-Through and Non-Pass-Through Syntax

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    Adeeb Mass'ad is offline Support Manager
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    Linked Servers: Pass-Through and Non-Pass-Through Syntax

    DESCRIPTION

    When working with Linked Servers, you can use the following methods to access your data:
    1. Non-Pass-Through syntax, where you compose your query as follows:
    select * from [Linked Server].[Data Source].[owner].[Table]
    2. Pass-Through syntax, using the OpenQuery function.
    Pass-Through syntax (openQuery) is always the faster method, because SQL Server simply sends the query to the OLEDB provider.

    When using the Non-Pass-Through syntax, SQL Server performs several processing steps, which can lead to some performance degradation:
    1. Deciding what part of the query can be delegated to the linked server.
    In this case you can use the Query Analyzer to get the execution plan, and check which part of the query got delegated to the Linked Server, and use this information to improve performance.
    2. Parsing the SQL statement.
    3. Getting schema information on each linked table: COLUMNS and INDEXES schema rowsets.
    For further Optimizing the query, you can also consult SQL Server's online help:
    • "Optimizing Database Performance"
    • "Application Design"
    • "Optimizing Distributed Queries".
    Last edited by Adeeb Mass'ad; 01-25-2007 at 09:53 AM.
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