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POHow does SQL Server handle SELECT statements in a transactional INSERT?
 

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  1. POHow does SQL Server handle SELECT statements in a transactional INSERT?
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    <p>As part of a retail closing process, there is a transactional stored procedure that selects from each of 18 tables and inserts them into a separate database for later mainframe processing. This procedure is showing some strange timing behavior, and I think it is because of a fundamental misunderstanding of the way transactions work in SQL Server.</p> <p>I recognize that this isn't the best architecture for this problem, and the new solution is being developed, but in the meantime, I need to improve this process.</p> <p>The stored procedure is running based on user request, and looks something like this:</p> <pre><code>BEGIN TRANSACTION INSERT INTO Table1 (Column1, Column2, Column3, Column4, Column5, Column6, Column7, Column8) SELECT Column1, Column2, Column3, Column4, Column5, Column6, Column7, Column8 FROM OLTPTable T INNER JOIN LookupTable1 L ON T.Foreign = L.Key INSERT INTO Table2 (Column1, Column2, Column3) SELECT Column1, Column2, Column3 FROM OLTPTable2 T INNER JOIN LookupTable2 L ON T.Foreign = L.Key INSERT INTO Table3 (Column1, Column2, Column3, Column4, Column5, Column6) SELECT Column1, Column2, Column3, Column4, Column5, Column6 FROM OLTPTable3 T INNER JOIN LookupTable3 L ON T.Foreign = L.Key -- Through Table 18 and OLTP Table 18 COMMIT TRANSACTION </code></pre> <p>The logging looks something like this:</p> <pre><code>Table1 0.2 seconds 354 rows Table2 7.4 seconds 35 rows Table3 3.9 seconds 99 rows </code></pre> <p>There isn't a clear correlation between quantity of rows or complexity of joins and time.</p> <p>My question is - on a long procedure like this, what is the effect of the transaction? Does is lock all the tables in the subselects at the beginning? One at a time? Is it waiting for the source table to be available for a lock, which is causing the waits?</p>
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    1. COWhy are you doing an inner join and not using any of the joined data? I see nothing but inserting from OLTPtable3 into table3, yet you have joined LookupTable3. Have you not added some of the Stored Procedure to your question or is it that complete for table3?
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    2. CODo you have indexes on all fields in joins?
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    3. CODo you need some kind of isolaton/concurrency handling over 18 table INSERTs? There are other ways if you can explain more...
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