This means that if the other transactions roll back, these rows may longer exist. that the transaction can read data that other transactions have not yet committed. This allows for what’s known as dirty reads, i.e. READ UNCOMMITTED is the least restrictive isolation level and is equivalent to using the NOLOCK locking hint on all tables. The isolation level is context specific if you set it in a stored procedure, it reverts to the connection’s previous state once the procedure exits. SET TRANSACTION ISOLATION LEVEL SERIALIZABLE The isolation level is set using a SET command. Here’s an overview of the different types of isolation levels available, to help you choose which one is best for you. Be too zealous, and you’ll end up troubleshooting deadlocks. Get too lazy and you’ll end up with phantom data and dirty reads. You (the royal you) run the risk of ingesting uncommitted data into your ETL.Isolation levels affect how aggressively SQL Server places and holds locks on tables and schemas. I have never tried this nor do I intend to. Note: never use NOLOCK query hints when selecting data from a table as an attempt to get around this. But, a fully blocking transformation will do the trick and eliminates the need for any additional indexes to the table (and the overhead that entails). You might be able to get creative with your indexing strategies here (I have not tried this). Otherwise, SSIS is attempting to INSERT data while there is a lock on the table/index. What this means is that the SELECT will be required to complete loading all data into the pipeline buffer before any data is allowed to pass down to the destination. If yes, then you're in luck - I have had this problem before.Īdd a sort to the data flow as this is a fully blocking transformation (see below regarding blocking transformations). If no, then a screenshot of the data flow tab would be helpful in determining the problem. My assumption here is that you are attempting to INSERT into the same table that you are SELECTing from. However, this does cause the SSIS execution to fail, so if it must be this way I'd like a cleaner, more graceful way to handle this situation.Ĭan anyone suggestion ways to, preferably, prevent the deadlock, or if not, then handle the error better?
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