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I'm doing a migration from Oracle to SQL Server and, for one of the tables where we have 3 million records, it is taking a lot of time to complete.

When I check the activity monitor, I can see the a wait type of PREEMPTIVE_COM_SEQSTRMREAD. Please help me understand what could be the issue.

I'm using linked server to connect Oracle from SQL Server.

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Linked servers are basically slow when huge data migration comes probably because memory required does not comes from buffer pool( this is not the case in SS 2012) there are other restrictions and bugs as well is your SQL Server patched to latest SP. You should probably choose SSIS for huge data migration. The wait type is related to OS doing some task its not directly related to SQL Server –  Shanky Jul 27 at 9:48

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To find out more about the PREEMPTIVE_COM_SEQSTRMREAD wait type I would read this great article at sqlauthority, but as Shanky said in the comments, SSIS would more than likely serve you better for a large migration.

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