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Subject Re: Tuning session replication on clusters
Date Thu, 06 Sep 2012 18:45:45 GMT
Rainer:  Thanks for the input.  I'll do some additional testing with the
sendAllSessions attributes, but my initial testing didn't show much gain.
If the rx/tx settings are already chunking up the session bytes into
smallish payloads then nothing I change with the sendAllSessions will
improve that.  I might be completely off base, but I'm unsure of what the
rxBufSize and txBufSize attributes do exactly, and if changing them would
boost throughput.

>One question:
>Plot those as X-Y in a spreadsheet and you'll see that it's only a bit
>worse than linear, especially after 1500. There's no enough data
>presented to draw an "exponential performance curve" conclusion:
>you're going to need more data to see if this is worse than linear.
>Can you collect more data? I know that creating 42k sessions of 700MiB
>each is probably a .. challenge, but more data would certainly be helpful.

Before I change anything (tuning) I'll do as much testing as I can tonight
to generate a data series and graph.  Btw, does this list support .ods/.xls
attachments?  I'm not sure how Tomcat handles building the object
containing all the sessions to send (Collection/List?), but it'll be
interesting to see if there are points where the basic nature of the
Collection object becomes less efficient.  The testing so far has already
shown that the quantity of sessions (like the 42k test I did in 901 ms on a
different app) doesn't appear to be an issue, while large session sizes do.
I know that the JVM was forced to make a full copy of all the session data
for the application inside heap space too, so after certain points I might
be reaching contention with memory management processes that handle heap
size, ratios, garbage collection, etc.

Having seen how quickly the JVM ramped up memory usage for replication, I'm
relatively confident the session aggregation and duplication into a new
Collection on the sender side is happening fast... reallllly fast.  I'll
try to get a protocol analyzer in place to capture the packets and compare
them to a basic file transfer of a single large file.

If anyone knows much about those rxBufSize and txBufSize settings and
whether they'll impact anything let me know.  If they operate like TCP
congestion and window sizes then adjusting them could have profound
performance implications.

Kyle Harper

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