Recently I received a very interesting question from my client who is a recently hired me for Comprehensive Database Performance Health Check. The question was a very simple but interesting one and I have decided to answer it with the proof and working demonstration. Here is the question – What is more optimal for the data load – Temp Table or Regular table? Why?
I am very sure that you might have encountered a similar question in the past. Lots of people who populate the data in ETL often wonder should they use Temporary Tables or Regular tables? The confusion starts because every single time they have to create a temporary table and in the end, it has to be destroyed, whereas the regular table always stays there and does not have to be re-created or dropped (just needs to be truncated).
Here is my answer to this confusion. If you have to load the data and do some transformation, I suggest you use Temp Table and not Regular Table, purely for the performance reason.
Before I go further writing about in this blog post. Let us do two different tests by measuring the statistics TIME.
Test 1: Data Load in Regular Table
Let us run the following script and measure the time of total execution.
SET STATISTICS TIME ON GO USE SQLAuthority GO -- Create Table CREATE TABLE FirstIndex (ID INT, FirstName VARCHAR(100), LastName VARCHAR(100), City VARCHAR(100)) GO -- Insert One Hundred Thousand Records -- INSERT 1 INSERT INTO FirstIndex (ID,FirstName,LastName,City) SELECT TOP 1000000 ROW_NUMBER() OVER (ORDER BY a.name) RowID, 'Bob', CASE WHEN ROW_NUMBER() OVER (ORDER BY a.name)%2 = 1 THEN 'Smith' ELSE 'Brown' END, CASE WHEN ROW_NUMBER() OVER (ORDER BY a.name)%10 = 1 THEN 'New York' WHEN ROW_NUMBER() OVER (ORDER BY a.name)%10 = 5 THEN 'San Marino' WHEN ROW_NUMBER() OVER (ORDER BY a.name)%10 = 3 THEN 'Los Angeles' ELSE 'Houston' END FROM sys.all_objects a CROSS JOIN sys.all_objects b GO DROP TABLE FirstIndex GO
Here is what we can see in the message window.
SQL Server Execution Times:
CPU time = 1454 ms, elapsed time = 1585 ms.
Test 2: Data Load in Temp Table
Let us run the following script and measure the time of total execution.
SET STATISTICS TIME ON GO USE SQLAuthority GO -- Create Table CREATE TABLE #FirstIndex (ID INT, FirstName VARCHAR(100), LastName VARCHAR(100), City VARCHAR(100)) GO -- INSERT 1 INSERT INTO #FirstIndex (ID,FirstName,LastName,City) SELECT TOP 1000000 ROW_NUMBER() OVER (ORDER BY a.name) RowID, 'Bob', CASE WHEN ROW_NUMBER() OVER (ORDER BY a.name)%2 = 1 THEN 'Smith' ELSE 'Brown' END, CASE WHEN ROW_NUMBER() OVER (ORDER BY a.name)%10 = 1 THEN 'New York' WHEN ROW_NUMBER() OVER (ORDER BY a.name)%10 = 5 THEN 'San Marino' WHEN ROW_NUMBER() OVER (ORDER BY a.name)%10 = 3 THEN 'Los Angeles' ELSE 'Houston' END FROM sys.all_objects a CROSS JOIN sys.all_objects b GO DROP TABLE #FirstIndex GO
Here is what we can see in the message window.
SQL Server Execution Times:
CPU time = 532 ms, elapsed time = 530 ms.
Comparision
It is very clear from the comparison that when we loaded the regular table it took around 1.5 seconds and when we worked with the temporary table it took around 0.5 seconds only. If you do not need your data to be persistent and you need for the temporary transformation, I strongly suggest that you use Temp Tables over regular tables.
The reason, temp tables are faster in loading data as they are created in the tempdb and the logging works very differently for temp tables. All the data modifications are not logged in the log file the way they are logged in the regular table, hence the operation with the Temp tables are faster. In the near future, I will write a detailed blog post explaining this behavior.
Reference: Pinal Dave (https://blog.sqlauthority.com)
