What might be causing increasing latency?

[Jannick Bitsch]

Hi

One possibility is that the effect is caused by
http://en.wikipedia.org/wiki/Nagle's_algorithm. Could be that the tcp stack
holds on  to the data with an increasing timeout algorithm, although that
doesn't really account for the variance. You can try to turn it off.

From
http://www.jboss.org/file-access/default/members/netty/freezone/api/3.2/index.html
:
ServerBootstrap b = ...;
b.setOption("child.tcpNoDelay", true);

I actually think you need to set if to false to turn nagle's algorithm off,
although that doesn't seem very intuitive :)

If that doesn't work, try to profile your gc and see if theres some
excessive object allocations or something, that could cause it to introduce
long pauses.


Regards
Jannick


2010/1/7 justkevin <filter.netty at wx3.com>

>
> After noticing my game app was occasionally running sluggish, I spent quite
> a
> bit of time trying to figure out why without success. If anyone has
> suggestions on what to try I'd appreciate it. The details are long, but I
> don't know what might be important:
>
> Details:
>
> The client is written in AS3.
>
> The server is written in Java using Netty 3.2 (I've updated to the most
> recent alpha).
>
> I'm testing locally, with client and server on the same box.
>
> When the first client connects, latency as measured with a round-trip ping
> pong is low, < 10 ms. It can remain low for a while, but eventually begins
> increasing in spurts at varying rates.  For example, it might be < 10 ms
> for
> a while, then 50-100 ms for a while, then 100-200 ms, and so forth. There's
> no upper limit, I've seen delays in multiple seconds. The larger the
> latency, the larger the variance. The increases may be correlated to large
> bursts of data.
>
> If I restart the client, the latency will usually drop, but not always.
> Sometimes it restarts high.
>
> If I restart the server, the next client to connect will get a low latency.
>
> Using system times, I've established that the latency is entirely on the
> downstream-- the ping takes 0ms to reach the server, and all the increase
> is
> between the time the pong is created and when its received by the client.
> >From this I'm guessing it's something with how I'm sending messages.
>
> The only ChannelPipeline handler on outbound is a LengthFieldPrepender.
>
> Here is how I'm sending the message:
>
>                // A Netty channel expects a message in the format of a
> ChannelBuffer:
>                ChannelBuffer buffer = ChannelBuffers.dynamicBuffer();
>                // Wrap the buffer with a ChannelBufferOutputStream, which
> implements
> DataOutput
>                // (our messages expect to write to a DataOutput)
>                ChannelBufferOutputStream output = new
> ChannelBufferOutputStream(buffer);
>                // First write the message id:
>                output.writeByte(message.getId());
>                // Then have the message write itself, checking to make sure
> the message
>                // obeys its length contract:
>                int beforeLength = output.writtenBytes();
>                int written = message.write(output);
>                if(beforeLength + written != output.writtenBytes()){
>                        logger.severe("Outbound message violated length
> contract:" + message);
>                        throw new RuntimeException("Message violated length
> contract:" +
> message);
>                }
>                // Finally, put into the channel. The channel pipeline
> should already have
> a length prepender:
>                this.channel.write(buffer);
>
> Thanks in advance for any suggestions,
> --
> View this message in context:
> http://n2.nabble.com/What-might-be-causing-increasing-latency-tp4269271p4269271.html
> Sent from the Netty User Group mailing list archive at Nabble.com.
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