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SQL 2012 AlwaysOn: Synchronous vs. Asynchronous commit. Performance impact

Recently I've had a chance to build a 3-server AlwaysOn environment distributed between the primary and secondary data centers.

The configuration looks like this:

Primary Data Center                         Secondary Data Center              
         SQLDEV1                                        SQLDEV3
         SQLDEV2


The availability group was crated with synchronous commit replicas on SQLDEV1 and SQLDEV2 and the replica on SQLDEV3 was configured for asynchronous commit.

The link between the data centers was not great and when I pinged SQLDEV3 from SQLDEV1 I got these results


Approximate round trip times in milli-seconds:
    Minimum = 39ms, Maximum = 63ms, Average = 42ms
I also created a very simple application that:
- generates a random INT
- if the table has a record with such key its updates the record otherwise it adds a new record to the table.
- every 5 seconds the app also records to a different (result) table StartTime, EndTime, and total number of inserts/updates

 And I query the result table and sum up totals updates occurred in past 10 seconds.

 I executed this application with 4 concurrent users from SQLDEV1 and the test database was also hosted on the same server.

 Then the test database was not a part of the availability group the average number of transaction per second was 5,500-6,000.

 When the test database was a part of the availability group with synchronous commit to SQLDEV2 and asynchronous commit to SQLDEV3 the average number of the transactions was 2,800 - 3,300

 And in the final test I changed the replica on SQLDEV3 to by in the synchronous-commit mode. And the average number of the transactions dropped to 40-60 per second (yes, decrease of two orders of magnitudes).

 Certainly, this is not a valid performance  tests but nevertheless it gives some feeling of the performace impact ones can expect when dealing with AlwaysOn.




Comments

  1. Dustin W. Jones3 April 2013 at 11:38

    would you be able share the tool you created for your test? Also, how did you measure transactions per second? I am working on a similar test myself.

    ReplyDelete
    Replies
    1. S.Mizrohi3 April 2013 at 12:17

      Hi Dustin,

      I've posted the script here

      http://smizrohi.blogspot.ca/2013/04/a-simple-script-to-test-server.html

      Let me know if it works for you

      Regards,
      Serguei

      Delete
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