SQL Server, temporary tables with truncate vs table variable with delete

Question

I have a stored procedure inside which I create a temporary table that typically contains between 1 and 10 rows. This table is truncated and filled many times during the stored procedure. It is truncated as this is faster than delete. Do I get any performance increase by replacing this temporary table with a table variable when I suffer a penalty for using delete (truncate does not work on table variables)

Whilst table variables are mainly in memory and are generally faster than temp tables do I loose any benefit by having to delete rather than truncate?

Answer 1

Running the followign to scripts, it would seem that the Table Variable is the better option

CREATE TABLE #Temp(
        ID INT
)

DECLARE @Int INT,
        @InnerInt INT
SELECT  @Int = 1,
        @InnerInt = 1

WHILE @Int < 50000
BEGIN
    WHILE @InnerInt < 10
    BEGIN
        INSERT INTO #Temp SELECT @InnerInt
        SET @InnerInt = @InnerInt + 1
    END
    SELECT @Int = @Int + 1,
            @InnerInt = 1
    TRUNCATE TABLE #Temp
END

DROP TABLE #TEMP

GO

DECLARE @Temp TABLE(
        ID INT
)

DECLARE @Int INT,
        @InnerInt INT
SELECT  @Int = 1,
        @InnerInt = 1

WHILE @Int < 50000
BEGIN
    WHILE @InnerInt < 10
    BEGIN
        INSERT INTO @Temp SELECT @InnerInt
        SET @InnerInt = @InnerInt + 1
    END
    SELECT @Int = @Int + 1,
            @InnerInt = 1
    DELETE FROM @Temp
END

From Sql Profiler

CPU     Reads   Writes  Duration
36375     2799937   0       39319

vs

CPU     Reads   Writes  Duration
14750   1700031 2       17376   

Answer 2

Quite frankly, with only 10 or 20 (or even 100) entries, any difference in speed would be in a sub-nanosecond realm. Forget about it - don't even waste a second of your brain time on this - it's a non-issue!

In general

• table variables will be kept in memory up a certain size - if they go beyond that, they're swapped out to disk in the tempdb database, too - just like temporary tables. Plus: if a temporary table has only a handful of entries, they'll most like be stored on a single 8k page anyway, and as soon as you access one of the entries, that entire page (and thus the whole temporary table) will be in SQL Server memory - so even here, there's really not a whole lot of benefits to table variables...

• table variables don't support indices nor statistics, which means if you have more than a handful of entries, and especially if you need to search and query this "entity", you're better off with a temporary table

So all in all : I personally use temporary tables more often than table variables, especially if I have more than 10 entries or something like that. Being able to index the temp table, and having statistics on it, usually pays off big time compared to any potential gain a table variable might have, performance-wise.