Scaling DB2 Connect parameter MAXAGENTS

In this test, one virtual CPU was defined for the DB2 Connect™ z/VM® guest and 1 GB memory was used. A constant load of 600 Trade 6 users was used. The parameter, MAXAGENTS, was scaled from 50 to 600 to scale the number of active connections between DB2 Connect and z/OS® DB2®. User connection requests that did not get one of hte active connections were queued within DB2 Connect. We used only one virtual CPU for the DB2 Connect because this is a scenario that creates a more moderate load.

The z/VM LPAR was assigned five CPUs and the z/OS LPAR was assigned six CPUs.

Figure 1 shows throughput for a DB2 Connect z/VM guest with one virtual CPU, scaling MAXGENTS from 50 to 600.

Figure 2 shows CPU utilization for DB2 Connect z/VM guests with one and two virtual CPUs, scaling MAXAGENTS from 50 to 600.

Observations

The DB2 Connect CPU utilization is near 100% in all cases. Between 50 - 200 MAXAGENTS, throughput is flat. With a MAXAGENTS value of 300 or more, the throughput increases according to the increase in active connections and then flattens out when it reaches the case where the connections are no longer concentrated. The CPU load on z/OS behaves in the same manner.

Throughput at 400 MAXAGENTS is 65% higher than throughput at 200 MAXAGENTS, even though DB2 Connect is running at almost 100% of available CPU.

Conclusion

The DB2 Connect connection concentration is a suitable feature to control the load on the database on z/OS. Of course, when it limits the number of connections, this prevents a further increase of the throughput, once the capacity of a single connection is exceeded. In this case a MAXAGENTS value of 300 will limit the CPU load on DB2 to a maximum of half of the 6 CPUs from that source.