![]() I wound up cancelling it this morning and working with a DBA to improve it. ![]() It turned out to perform very slowly, taking 12 hours to process 25M of 33M rows. I encountered this thread yesterday and wrote a script based on the accepted answer. So, if you don't have an index that can be used for this operation, and can't temporarily create one that will actually work (a filtered index might work, depending on your WHERE clause for the UPDATE query), then try the approach shown in answer (and if you use that solution, please up-vote it). For inserting into #targetIds, use INSERT INTO #targetIds (column_name(s)) SELECT and remove the ORDER BY as it's unnecessary.For the #batchIds table, declare a clustered primary key on the column(s).For the #targetIds table, declare a clustered primary key on the column(s).Explicitly create the #targetIds table rather than using SELECT INTO.The approach shown in that answer is a very effective pattern that I have used myself on many occasions. (It's important to capture and join on the clustered index columns, whether or not those are the primary key columns!). The updated method copies the IDs for all rows to be updated into a temporary table, then uses that temp table to INNER JOIN to the table being updated on the clustered index key column(s). This is the situation that encountered, thus requiring a different approach. there is an index, but at least one column in the WHERE clause is a string data type that does not use a binary collation, hence a COLLATE clause is added to the query here to force the binary collation, and doing so invalidates the index (for this particular query).there is no index to support the query, or.For tables of at least a certain size (which varies due to several factors so I can't be more specific), performance will degrade as there are fewer rows to fix if either: I emphasized "better" above (as in, "this is a better model") because this has several improvements over the O.P.'s original code, and works fine in many cases, but is not perfect for all cases. I also added a condition to the WHERE clause to prevent rows that have already been updated from being updated again. Only in those cases where the final set of rows is equal to will this code run a final UPDATE affecting 0 rows. insensitivity of case, accent, etc, or linguistic equivalence.īy testing against you can avoid that final UPDATE query (in most cases) because the final set is typically some number of rows less than in which case we know that there are no more to process (which is what you see in the output shown in your answer). that you don't skip differences that compare the same due to Use a binary Collation (ending in _BIN2, not _BIN) to make sure SET = - initialize just to enter the loopĪND tab.Value 'abc1' COLLATE Latin1_General_100_BIN2 I suspect that the real WHERE clause is not being shown in the example code in the Question, so simply relying upon what has been shown, a better model (please see note below regarding performance) would be: DECLARE INT - keep below 5000 to be safe Please see my answer on DBA.StackExchange for a TRY / CATCH template that handles transactions:Īre we required to handle Transaction in C# Code as well as in Store procedure auto-commit).Īssuming you find a reason to keep the explicit transaction, then you do not have a TRY / CATCH structure. It complicates the code and you have no handling for a ROLLBACK, which isn't even needed since each statement is its own transaction (i.e. There is no purpose in having an explicit transaction here. ![]() The ROWCOUNT option does not affect dynamic cursors, but it does limit the rowset of keyset and insensitive cursors. Setting the SET ROWCOUNT option causes most Transact-SQL statements to stop processing when they have been affected by the specified number of rows. It can affect more than just the statement you are dealing with: For a similar behavior, use the TOP syntax Avoid using SET ROWCOUNT with DELETE, INSERT, and UPDATE statements in new development work, and plan to modify applications that currently use it. Using SET ROWCOUNT will not affect DELETE, INSERT, and UPDATE statements in a future release of SQL Server. It has that been deprecated since SQL Server 2005 was released (11 years ago): You should not be using SET ROWCOUNT to limit the number of rows that will be modified. So it is safest to keep it just below 5000, just in case the operation is using Row Locks. The issue is that Lock Escalation (from either Row or Page to Table locks) occurs at 5000 locks. You should not be updating 10k rows in a set unless you are certain that the operation is getting Page Locks (due to multiple rows per page being part of the UPDATE operation).
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