APS AU4 Feature Review: Introducing Round Robin Distribution

This is our second post covering the new features and improvements included in the SQL APS PDW AU4 release. 

Starting with AU4, tables in PDW now have a third distribution option.  In addition to the familiar Hash distribution and replicated formats, AU4 introduces the Round Robin distribution type.  This distribution type was first introduced in the SQL Data Warehouse Service and has now made it into the PDW workload. I would recommend reviewing the content on the SQL Data Warehouse Documentation site, as almost everything applies to the appliance as well and is a great explanation of the feature.  The main difference being for the appliance the default distribution method will remain to be replicated.  Tables will only utilize the ROUND ROBIN distribution type if it is specified in the create command. 

While Round Rodin distribution will get even distribution and eliminate skew, it will not be distribution compatible for a large number of scenarios.  It is very likely that joins and aggregations to distributed tables or other round robin tables will require data movement.  It is recommended to use this distribution type when you are beginning a migration to PDW and do not yet know of a good distribution key, or when no good distribution key exist for a large table.  If queries against round robin tables contain predicates which greatly reduce the amount of data to be moved, it is possible the even distribution may be enough benefit to warrant permanent use. 

Example Syntax:

CREATE TABLE round_robin_test
col1 int,
col2 varchar,
col3 int



Like other distribution formats, it will take testing in your specific environment to find the best combination of distribution methodologies to get optimal performance.


The first post in this series can be found at:



Please check back for future posts!

Comments (2)

  1. Subramanian kaushik Gurumoorthy says:

    Hi Tim,

    Thanks for the post.

    I checked for the APS upgrade procedure across all the Microsoft sites and Books online.

    But could not find the same.

    Kindly do inform if  we have any official documentation or links to upgrade procedure as our customers is planning  for an upgrade.

    Thanks for your help..


    Subramanian kaushik Gurumoorthy

  2. Hello,

    APS Upgrades are performed by MSFT field engineers and are usually included with your support contract.  You can contact your Technical Account Manager at Microsoft to begin the planning process.  Please feel free to contact me directly if you have any issues:


Skip to main content