Let me try to summarise the answers as per the commenters above.
First of all, to achieve higher deletion speeds you can do three things:
- Delete a higher number of rows at a time
- Use partitioning
- Run multiple deletes
Ad 1) Since deleting a large number of rows at a time hit the transaction log hard and causes locking - you likely want the number of deletes in a statement to be "small". I find that around 10K rows is a good number (and having table lock escalation turned off with
ALTER TABLE Foo SET LOCK_ESCALATION = Disabled
Ad 2) If your table is not already partitioned, this is not an option
Ad 3) DELETE in SQL Server is single threaded, so you need to run more than one at a time to get max speed. To run multiple deletes concurrently, you need a way to partition them so each parallel delete runs on its own set of keys and doesn't block with the others. Typically, you can use the primary key of the table to partition the delete.
For example, if you have an IDENTITY column called
key on the table, you can first:
SELECT MAX(key) - MIN(key), MIN(key) FROM Foo WHERE <rows that must be deleted>
Keep the Max - Min and Min somewhere (a table in tempdb) that you can quickly read from into variables
Let us say you decide that you can allocate 4 cores for running deletion. You now run 4 queries, either from 4 x SSMS new query or four command prompt via SQLCMD, each doing this:
DECLARE @NumDone INT = 1
WHILE @NumDone > 0 BEGIN
SET ROWCOUNT 10000
DELETE FROM Foo WHERE Key BETWEEN @MinKey + @IntervalSize / 4 * @n
AND @MinKey + @IntervalSize / 4 (@n + 1)
SET @NumDone = @@ROWCOUNT
Pick @n = 0,1,2,3 for each of the concurrently running DELETES.