[undertow-dev] TransferTo/sendfile Undertow v1.0.x vs 1.1.x

[Stuart Douglas]

I have filed https://issues.jboss.org/browse/UNDERTOW-407 and pushed a potential fix for this upstream to both the master and 1.1.x branches. Can you try it out and see if it resolves your issue?

Stuart

----- Original Message -----
> From: "Dave O'Brien" <davidpobrien at gmail.com>
> To: undertow-dev at lists.jboss.org
> Sent: Friday, 13 March, 2015 10:33:43 AM
> Subject: [undertow-dev] TransferTo/sendfile Undertow v1.0.x vs 1.1.x
> 
> Hi everyone,
> 
> I wanted to run this 'issue' past the experts, as I've looked into it myself
> and hit a bit of a dead end.
> 
> Our application is using Undertow 1.0.17 for serving both static and dynamic
> Web content. We did some benchmarking early on in the development of our app
> and got some very impressive results.
> 
> On a modest server with undertow 1.0.17, using wrk defaults we get around 50k
> rqsts/s for a 2kb file and about 17k rqsts/s for a 100kb file. So far, so
> (very) good.
> 
> I recently tried updating to version 1.1.2 and ran the original tests and got
> similar results as for v1.0.17 for the 2kb file. For the 100kb file, however
> the throughput dropped to about 10k rqsts/s.
> 
> Not the end of the world, I know but I decided to dig around and see what was
> (or wasn't) going on....
> 
> Our app has a sendfile threshold (64k), that above which we use the
> ResponseChannel 'TransferTo' method, which performs (on Linux anyway) a
> native zero-copy sendfile operation using the Java NIO
> FileChannel.transferTo call (which calls into Linux sendfile under the
> covers if certain conditions are met).
> 
> In v1.0.x, the native sendfile method (transferTo0) is ultimately invoked to
> send the content. But in v1.1.x (and 1.2.x also) the transferTo method in
> the FileChannel instead opts to invoke transferToArbitraryChannel which
> resorts to a kernel -> user space copy and a not-insignificant drop in
> throughput.
> 
> So my question is, is this change across the versions deliberate, a sacrifice
> for improvements elsewhere - or is it a bug?
> 
> If it's a bug I'm happy to re-instate the native sendfile functionality
> myself, but I wanted to check it was an issue first...
> 
> Thanks in advance for any assistance/advice on this one...
> 
> David.
> 
> 
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