Why does the Cache Transform in SSIS have a file cache option? When would I use this, especially when compared with using the default option which is to store the results in memory? One downside of the default option of storing the results in memory is that the cache is cleared immediately once the package is completed and that memory cache cannot be shared among other packages.

However, the File connection option will allow the results to be reused among multiple packages. But hold up, that’s not quite as good as you might think, each package still must read from the file and then subsequently load that file into memory!

So why are we discussing this if it’s essentially doing the same thing as the default option? Good point, and well received, did you read the title?

Imagine now that you have a rather large table that you need to access many times during your nightly ETL, this is very common in data warehousing situations. You can now lessen the effect of a poor performing network by using the file cache option in the cache transform. You can bring the data across the network only once, load it into a file, and in the future you can reference that file on your local machine and avoid  going across the network. As you can imagine this can be quite advantageous!

Set up is quite simple as well, see below:

1. Bring the cache transform into your data flow and connect it to your source.
2. Open the cache transform for editing.
3. Select NEW for cache connection manager.
4. 
5. Select “Use file Cache” and then browse to the location where the file will be stored.
6. Next click the Column tab at the top and specify at least one index column.
7. 
8. Click OK, map the columns, Click OK to close out the transform.

Now that the initial set up is complete I will demonstrate how to reference this file:

1. In the next data flow I set up an OLE DB source and connection that output to a Lookup transform.
2. Inside the lookup transform select “Cache Connection Manager” on the general screen.
3. 
4. On the connection screen select your cache connection manager from the drop down list.
5. 
6. And that’s it!, set up the rest of  your lookup transform like you normally would.

Thanks for looking!

There are quite a few different scenarios for when cache transforms can be used to improve usability and performance inside SSIS. In this post I am going to quickly outline a scenario where cache connection managers can greatly improve performance when loading a fact table.

During the pre-execution phase of package execution SSIS “caches” the lookups inside your package into memory, unfortunately if you are using OLE DB connections in your Data Flow Task this caching happens in a serialized format (one after the other). Typically this isn’t a big deal because you may only have one or two large dimension lookups and all others are very small in size and very fast. But what if this isn’t the case? What if you have 5, 6, 7, or more dimensions all with millions of records that you must cache before the package begins execution? Here is how we can get around this little issue.

• We can have all of our lookups cached in parallel if we use the cache transform in a data flow task prior to the loading of the fact load. If you have never used the cache transform before you can find a quick demo here: http://beyondrelational.com/modules/2/blogs/82/posts/13209/msbi-60-ssis-24-data-flow-task-10-cache-transform-task-detailed-information-amp-explanation-with-exa.aspx

• Inside the data flow tasks we will set each source to point to our cache transforms. Each one of the Cache Transforms will require a connection manager to store the data.

• Below is a screenshot of the connection managers created by the Cache transforms:

• Now that the cache connection managers have been set up, you will need to point each of your lookup transforms to the “Cache Connection manager” instead of the default of  OLE DB connection manager.

• Now to the last step. Now click on the connection tab and point to the cache connection manager that stores the information for your lookup:

• All other configuration steps are the same as normal. Thanks for looking, and hope this helped.