Monday, February 25, 2019

Db2 for z/OS: Isolating REST Client Activity in Db2 Monitor Accounting Reports

In an entry posted to this blog some years ago, I described the form of a Db2 monitor-generated accounting report that I most like to use to get an overall view of application activity in a Db2 for z/OS environment: an accounting long report with data ordered by connection type (here, I am using terminology associated with the Db2 monitor with which I'm most familiar: IBM's Tivoli OMEGAMON XE for Db2 Performance Expert on z/OS). I like to see data in an accounting report aggregated at the connection type level because within such a report there is a sub-report with detailed accounting information for each connection type through which the target Db2 subsystem was accessed: a sub-report showing all CICS-related work for the subsystem, one showing all TSO attach-related work, one showing all DDF-related work, etc.

Now, the thing about the DDF-related activity in this form of an accounting report is that it is presently - thanks to a recent and important Db2 for z/OS enhancement - kind of mis-labeled. The DDF-related work in an accounting long report with data ordered by connection type is distinguished by the label CONNTYPE: DRDA. How is that a bit misleading? Well, the native REST interface to Db2 for z/OS (the enhancement to which I referred previously - designed into Db2 12 and retrofitted to Db2 11) is an extension of the Db2 distributed data facility (DDF's long name). What that means - as pointed out in a blog entry I posted a few months ago - is that there are now two paths into DDF: the DRDA path (which application developers might think of as the SQL path) and the REST path; thus, CONNTYPE: DRDA is a little off because what you see in that part of an order-by-connection-type Db2 monitor accounting report is all DDF-related activity on the Db2 subsystem of interest - activity associated with DRDA requesters and activity associated with REST clients.

What should the designator of DDF-related activity in an order-by-connection-type Db2 monitor accounting report be? CONNTYPE: DRDA+REST? CONNTYPE: DDF? Or, should there be a CONNTYPE: DRDA for work that is strictly related to actual DRDA requesters and a CONNTYPE: REST for activity related to REST clients?

I'll let the Db2 monitor developers figure that out. Meanwhile, if you have a Db2 subsystem on which there is a good bit of activity related to both DRDA requesters and REST clients, and you want to see, in one Db2 monitor accounting report, just the REST-related activity, how can you do that? If all the REST clients authenticated to the Db2 subsystem using only two distinct authorization IDs - for example, ABCID and XYZID - then you could get your REST-only accounting report by telling the Db2 monitor to include, in the accounting report, only activity related to those primary authorization IDs. The way you'd convey that request to OMEGAMON for Db2 would be through this specification in the report control statement:


Obviously, that approach becomes unwieldy if there are, say, a hundred or more IDs used by Db2 REST clients.

Is there a better way? Yes, there is. It so happens that a Db2 accounting trace record associated with a REST client interaction will include, in the correlation ID field (the field name is QWHCCV), the value 'DB2_REST'. Thus, one can easily get a Db2 monitor accounting report showing all REST-related activity for a subsystem, and only that activity, by informing the monitor that the report should include data only for DDF-related requests for which the correlation ID value is DB2_REST. Again using OMEGAMON for Db2 report command syntax (which is what I know), that would be done with this specification:


And there you have it. I hope that this information will be useful to you, should your site start seeing a significant amount of Db2 for z/OS access via the REST interface (and I think that a substantial number of sites will see just that in the near future - the REST interface has generated a lot of interest among application developers).

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