diagnosing vbj performance problems
Below is information on how to diagnose and alleviate several VBJ
performance problems.
To diagnose VBJ performance problems, run your program
with java -verbosegc. Generally, the JVM should initiate garbage collections after
several minutes or longer. If you are seeing garbage collections which occur many
times per minute, you can benefit by modifying the defaults provided with VBJ.
The ORB creates a separate GarbageCollector thread that runs every 30 seconds
by default. This thread is responsible for maintaining various ORB data,
specifically, weak references. The thread calls System.gc()
each time it runs. The flags that control this behavior are ORBgcTimeout and
ORBsyncGC. The two flags work independently, so both, one, or neither can be
specified.
ORBgcTimeout is the waiting time in seconds of the thread. Setting this to a larger
number should decrease the frequency of these types of garbage collections.
ORBsyncGC can be set to false to prevent the direct call to System.gc(). The
GarbageCollector thread will still run but will skip the call to System.gc().
For example: vbj -DORBgcTimeout=300 -DORBsyncGC=false Server
This should decrease the frequency of the GarbageCollector to every five minutes,
and eliminate forced System.gc() calls.
The only other time that the ORB might call System.gc() directly is when it catches
an OutOfMemoryError when reading a byte array as part of the marshaling
process for messages. Seeing this frequently means that you probably have corrupted messages rather than a large data stream. The ORB also prints out a
diagnostic message when this occurs: "Forcing garbage collection due to limited
memory...".
problem: poor performance when sending messages to a server
A small ORBtcpTimeout setting forces the client to break the current request. The
ORBtcpTimeout is used with the underlying socket using the setSoTimeout()
method. When using a 200ms value on a test that is a stress test, the client side of
the connection breaks out after 200 ms each time a server reply is not received
within 200 ms. The exception is remapped to a CORBA.TRANSIENT and
caught by the client stub. If the value is increased to 800 ms the problem should
occur less frequently. Normally, Inprise advises customers to be very conservative
(i.e., use high values, 1000 to 2000 ms, or larger than the anticipated server
response time) with this option to catch true anomalies. The alternative, breaking
out and resending the request is often much worse than waiting an additional
second to see if the server is truly not responding.
Marshaling errors can be a consequence of broken connections. In VBJ, broken
connections exposed a thread-related defect on the server side ORB that allowed
two threads to modify the same marshal buffer. The problem is more common with
native threads. The problem is fixed in VBJ 3.3.1 and VBJ 3.4. In VBJ 3.4, a low
value for ORBtcpTimeout may still show InterruptedIOException exceptions
whenever the client side ORB breaks out and resends the request, but the server
side bug will not result in a marshal buffer corruption.
problem: poor performance when client and server on same machine
If your client and server are on one machine, you may benefit from using the
TCP_NODELAY option. We only recommend this if you are on a single machine
using the loopback network.
setting vbj properties from within your program
These are example values -- you will want to adjust these to obtain the best
performance on your system using the guidelines outlined previously.
// set up some ORBs and BOAs;
orbprops= new java.util.Properties[NumLANs];
orbprops[0]= new java.util.Properties();
orbprops[0].put("ORBtcpTimeout", "2000"); // Send time-out - 2 sec
orbprops[0].put("ORBtcpNoDelay", "true"); // Set TCP_NODELAY
orbprops[0].put("ORBsyncGC", "false"); // No sync GC
orbprops[0].put("ORBgcTimeout", "300"); // 5 minutes, as above
orbprops[1]= new java.util.Properties();
orbprops[1].put("ORBtcpTimeout", "2000");
orbprops[1].put("ORBtcpNoDelay", "true");
orbprops[1].put("ORBsyncGC", "false");
orbprops[0].put("ORBgcTimeout", "86400"); // a bit high - 24 hours
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