[xSocket-develop] scalability and latency

[James O. <Jam...@co...>]

I'm experimenting with xSocket 2.0-beta-2 and xSocket-http 2.0-alpha-4
to implement a messaging server that pushes messages to http clients.
The messages are small (approx 15 bytes) but frequent (enqueued at a
rate of 25 per second per client).  These messages are in 10 logical
topics and only the latest available message from each topic is sent,
i.e. when a new one is queued to be sent it overwrites any message
already queued for the same topic.  The server infrastructure will also
concatenate several smaller messages to make one larger message if
messages are available on multiple topics at the time of writing to the
BodyDataSink.  Thus the number of messages dequeued and sent to the
clients is automatically throttled by the capability of the underlying
comms.

 

I have the same setup with Tomcat 6 using the NIO connector and find
that I can add large numbers of users and still get good performance.
With the hardware I have it can deliver 70,000 messages per second.
More users mean fewer messages per user but the overall throughput
remains the same and latency is low and fairly consistent.

 

However I'm finding that this does not scale as well with xSocket.  The
max message throughput is lower and reduces as more clients are added.
The average latency is higher and can be highly variable (>10 seconds!)
depending on the number of background message writing Threads and the
number of Dispatchers.  Making the number of message writing Threads
equal to the number of Dispatchers and keeping them both quite low (<=
3) reduces the latency variability but the average is still
significantly higher than with Tomcat.  SYNC flushing is also better
than ASYNC with this setup because it causes more message concatenation
(fewer larger messages sent).

 

The xSocket API has been a joy to work with and allows me to do more
than with Tomcat/Comet (e.g. if desired the client can continue to write
to the connection) and the memory use is incredibly low, however the
performance for my scenario is worse than I was expecting.

 

Is there something I might be missing in my config or is this not a
scenario that xSocket is currently optimal for?




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