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Re: Need slow web client

by rjt (Deacon)
on Mar 21, 2013 at 10:22 UTC ( #1024710=note: print w/ replies, xml ) Need Help??


in reply to Need slow web client

Before I get into Perl specifics, I would highly recommend you take a look at Net::Packet::Dump or plain old tcpdump if you're on a compatible system, so you can see what's actually going on between client and server at a packet level. Simply slowing down the client may not have much bearing on the server/proxy, as the TCP/IP stack will buffer sent packets, intermediate routers can shape traffic, and the specific behavior of your proxy (including network settings in the OS/kernel) can have a great impact.

Particularly if you are serving small requests, the speed of the client may have little to do with freeing up the server process, and main thing you free the server process from in any case is an open socket, which may or may not be significant. If you think you're also freeing up server RAM or CPU cycles by offloading to a proxy, I'd urge you to benchmark this thoroughly before introducing another hop into your architecture, if you haven't already done so.

You talk about freeing the "server process". If your use of the word "process" implies that the proxy would be another application running on the same (virtual) machine, benchmarking will be even more important.

I know I'm now way off-topic from a Perl point of view here, but we PerlMonks pride ourselves on being equal opportunity discussors sometimes. :-) The short version is: when trying to squeeze performance from network servers, I've found thorough network and server analysis under load is the only way to go. I'd like to know more about the analysis you've done, as there are many different ways to load test applications, and many definitions of "slow client" (the usual suspects being limited bandwidth, high latency, packet loss, combination of all three).


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Re^2: Need slow web client
by McA (Curate) on Mar 21, 2013 at 10:37 UTC

    Thank you for your comment. But I really want to do a synthetic check whether the proxy is buffering (like promised) the output of the application server (which resides on a different machine). I do agree that this behaviour is only meaningful with returning big responses.

    Personally I like this kind of comment hopefully broaden someone's view.

    McA

      But I really want to do a synthetic check whether the proxy is buffering (like promised) the output of the application server (which resides on a different machine).

      Maybe I'm missing something, but can you simply check the web server logs to confirm the request came from the proxy instead of the endpoint? And/or check the proxy logs (perhaps increasing the log level for server connection/caching details)? That should at least answer that question. Most proxies also allow you to customize HTTP headers to some extent, so you can even stick some metadata in there to help get more objective results in your testing.

      For a very simple "slow client", the LWP::UserAgent callback suggestion is reasonable for a starting point.

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