Databases Reference
In-Depth Information
When using a distributed queue, a shared filesystem such as a
Storage
Area Network
(
SAN
) should be used to hold the distributed queue files
so that they are available to the managed server when it is restarted on
another physical machine.
WebLogic JMS also supports database queues. If stored in an Oracle
Real
Application Clusters
(
RAC)
database these can provide a high degree of availability,
but there may be contention issues for the queue tables when large numbers
of managed servers are all accessing the same shared queue. Hence the Oracle
recommendation is to use distributed queues with a resilient file-based backing
store, ideally on a SAN, so that it can easily be shared between multiple machines.
Testing considerations
When testing a cluster, it is important to ensure that requests are distributed
across the cluster in a fair manner. This is important to make sure that there are no
unexpected behaviors when requests for the same composite instance are distributed
across several nodes in the cluster.
Avoid IP stickiness
When using a load balancer during testing, it is important to avoid the
use of a load balancer set up to use IP stickiness. IP stickiness is used to
route requests to servers based on the IP address of the client. This is
bad when testing, in particular, because the request will tend to come
from a small number of load injectors, and this will cause all requests
from a single injector to hit a single server. This can mask problems that
only show themselves when the same composite is executed on multiple
servers. Note that HTTP cookie stickiness is a good idea, however, as
it allows correct operation of several components including the human
workflow engine and the consoles.
Often, we will use a composite to test other composites. In this case, we need to
make sure that the test harness composite makes external calls through the load
balancer to all the services it invokes. We can do this by setting the endpoint address
to be different from the configured property on a reference. This ensures that the
test mimics the real world more closely. Failure to do this will mean that the test
will be using the optimized internal transports and hence show better performance
characteristics than might be expected in production.
