SQL Server 2008 R2 – How to Speed Up Looped INSERT INTO Statements

hintsinsertperformancesql-server-2008-r2

I currently use the following statement, for 10,000 rows it takes about 150 seconds. I tried removing the index on the target table, but this didn't help. Running the loop without the INSERT INTO takes less then 50ms. I need it to update about 300 million rows and I can't really wait 52 days (!) for it to complete.

Bottom line of the following update query is that I need to go over each row, perform calculations on a VARBINARY and extract proper values from it (we need to get rid of the packed VARBINARY fields), and store that in a new table.

FETCH NEXT FROM LocCities INTO @LocCity 
WHILE (@@FETCH_STATUS = 0)
BEGIN
    -- several sets, removed calculations for clarity
    SET @LocationId = Calculation1()
    SET @CityId = Calculation2()

    IF(@LocCity <> 0)
    BEGIN
        -- left out an inner loop here on the VARBINARY based on its length
        INSERT INTO LocationCities (LocationId, CityId)
        VALUES (@LocationId, @CityId)
    END
    FETCH NEXT FROM RespCursor INTO @TuningRow
END

I understand that I can use the WITH keyword with table hints, but I am not sure what to use. I expect the final update query to run in several hours, and hope there's a way to do that. I really can't wait almost two months ;).

Isn't there something similar like BULKINSERT that I can use?

Best Answer

I really don't think table hints or BULKINSERT are going to help you here - your approach is still to process each varbinary value one at a time, and this will be your downfall regardless - especially when you discard the idea of set-based queries because you "don't think it's possible."

Here's a set-based approach with no awful loops or cursors. This assumes that the pattern is always the same (LocationID is the first byte, and CityID is the next two).

DECLARE @x TABLE(x VARBINARY(32));

INSERT @x VALUES(0x010734),(0x030735040736),(0x030742050743060712);

;WITH n(n) AS 
(
  SELECT TOP (300) (number*3)+1 
  FROM [master].dbo.spt_values -- your own Numbers table is better
  WHERE [type] = N'P' ORDER BY number
)
-- INSERT dbo.LocationCities(LocationId, CityId)
SELECT 
  x.x,      -- comment this out before insert 
  LocationID = CONVERT(INT, SUBSTRING(x.x, n, 1)),
  CityID     = CONVERT(INT, SUBSTRING(x.x, n+1, 2))
FROM @x AS x INNER JOIN n ON LEN(x) > n.n;

Results:

x                        LocationID    CityID
---------------------    ----------    ------
0x010734                 1             1844
0x030735040736           3             1845
0x030735040736           4             1846
0x030742050743060712     3             1858
0x030742050743060712     5             1859
0x030742050743060712     6             1810

Some articles that will help you understand numbers tables and why generating sets in SQL Server is far superior to even the most efficient loop you can derive.

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