Partitioning

Over the past few years I have implemented partitioning a number of ways.  In the world of SQL Server 2000, it was “home-made”.  Meaning that I would create a number of tables whose schema was identical, create check constraints and then link all of the data together with views.  This method had tremendous upside, but as you can imagine, the overhead ov moving data from one “partition” to another was very time intensive and expensive from an I/O perspective.

With SQL Server 2005, Microsoft introduced partitioning as part of the relation engine… This was huge news for me specifically.  I could actually do this “Right” for my clients.  As many of you know, paritioning has some limitations in SQL Server 2005 that made a great option, but the limitation of parallelism that accompanied the feature left for a bad taste in the mouths of many.

This brings us to SQL Server 2008 where, based on my testing, the parrallism issue is truly resolved and the optimizer is actually recoqnizing the partitions as it should. 

So, what have I done?  I’ve implemented it all over the place.  That is the point of this post.  At one client, it’s worked just as I imagined that it would… at another, I’ve had a bit of stumbling block.  I did not realize the impact that non-clustered indexes would have if they weren’t created with the partition.  So what I ended up with, over time were very, very, very heavily fragmented indexes.  In fact, some of them were so bad that the optimizer was choosing different paths to the data.  (That’s B.A.D.).

I thought my fix would be a tough one.  But it turned out to be uber simple.  I dropped the indexes that existed on the primary filegroup and re-created them on the partition.  Viola, piece of cake.  Everything was awesome, until about 2 weeks later when the fragmentation of those indexes caught up with me.  This left me cursing the amount of time it was going to take to rebuild these huge indexes and wondering how often I’d have to do it…

So, I stopped trying to do it my way and went to my favorite resource.  BOL.  Of course, there is a way to do this and it’s not painful.

It’s the function $PARTITION.  If you are using partitioning in your environment and you are unaware of this function, become aware. 

What this function enabled, in a very easy and straight foward manner was for me to quickly and dynamically identify which partition was the active partition.  Once I had that information, I simply wrote an alter index statement with rebuild where the partition equaled my variable value.

Code snippet below.

Declare @PartitionID INT

Select @PartitionID  =  (SELECT $PARTITION.PartitionName (getdate()));

ALTER INDEX IndexName ON owner.TableName

REBUILD Partition = @PartitionID;

    —  Note that I can utilize the getdate function with the $Partition function.  Since my partition function (key) is a datetime value.  Simple logic could be used if it were an int.

The obvious advantage to this is that when I run the rebuild index script, it is only running for the active partition.  This brings down the amount of time required for this action and enables me to run it nightly as the data becomes very fragmented from day to day in the current partition.

So, my lesson for this day?

Easy, think ahead about what will happen down the road.  Always check BOL and test, test, test. 

Happy Partitioning!

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