Partitions Accessed and Partition Range in the Query Execution Plan

Let’s say you are querying a partitioned table and you would like to see which partitions were accessed by looking at the graphical execution plan:

“Actual Partition Count” shows a value of 1 and “Actual Partitions Accessed” shows a value of 50.  The “Actual Partitions Accessed” property name could cause confusion though, since what you’re actually looking at is the partition numbers accessed (not the count of partitions accessed). 

I prefer the XML naming convention instead:

  <PartitionsAccessed PartitionCount="1">
    <PartitionRange Start="50" End="50" />
  </PartitionsAccessed>

The name mapping is as follows from Graphical-to-XML Plan formats:

“Actual Partition Count” = PartitionsAccessed element & PartitionCount attribute

“Actual Partitions Accessed” = PartitionRange

If I modify the query to access two partitions, I see the following (graphical and XML plan output):

<PartitionsAccessed PartitionCount="2">
               <PartitionRange Start="1" End="1" />
               <PartitionRange Start="50" End="50" />
</PartitionsAccessed>

And here is an example accessing all partitions in the table:

<PartitionsAccessed PartitionCount="63">
    <PartitionRange Start="1" End="63" />
  </PartitionsAccessed>

Once you realize the mapping, its no big deal to understand what’s going on, although I do see it causing confusion (hence this blog post).