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From sebb <seb...@gmail.com>
Subject Re: Bug 56119 - dealing with idle connection timeout and dropped connection
Date Wed, 19 Feb 2014 21:51:41 GMT
On 19 February 2014 21:03, Philippe Mouawad <philippe.mouawad@gmail.com> wrote:
> On Wed, Feb 19, 2014 at 9:58 PM, sebb <sebbaz@gmail.com> wrote:
>
>> On 19 February 2014 18:49, sebb <sebbaz@gmail.com> wrote:
>> > It looks as though the problem reported in Bug 56119 was due to the
>> > server dropping connections that have been idle too long.
>> >
>> > There may also be servers that only allow a connection to be reused a
>> > certain number of times (this does not seem to have been the case
>> > here).
>> >
>> > This email is to discuss what JMeter could perhaps do to make it
>> > easier to test such servers.
>> >
>> > The two existing work-rounds are:
>> > - disable Keep-Alive
>> > - enable staleCheck
>> >
>> > Neither is ideal; the first is awkward to use, and staleCheck can
>> > generate unnecessary additional traffic (which is why it was disabled
>> > in 2.11).
>> >
>> > I can think of two possible approaches:
>> >
>> > 1) proactively shut connections. This would be easy for servers that
>> > limit reuse.
>> > Just count reuses and turn off keep-alive when a specified limit is
>> reached.
>> > Not so easy for idle timeouts; one cannot retroactively disable
>> keep-alive.
>> >
>> > 2) Deal with the disconnects when they occur.
>> > The code needs to distinguish which errors are retriable, and may need
>> > to distinguish at what point the failure occurs. For example, even a
>> > POST ought to be retriable if JMeter is unable to send any data on the
>> > connection.
>> >
>> > Also need to consider how one might report retries.
>> > I think the tester needs to be able to find out if additional requests
>> > have been made by JMeter.
>>
>> Further testing against the ASF servers shows that HC 4.2.x does
>> handle idle timeouts without needing to use the staleCheck option.
>> This relies on the server sending a header of the form:
>>
>> Keep-Alive: timeout=5, max=100
>>
>> In this case, the connection is automatically recreated if necessary
>> when the next sampler runs.
>> If the server fails to send the header, then the connection may be
>> dropped unexpectedly (which is what was happening with Bug 56119).
>> So another approach might be to allow an optional keep-alive timeout
>> in case the server does not provide one.
>>
>> Or we could take the view that there is nothing to fix in JMeter.
>> The Keep-Alive header is there for a reason, it tells the client when
>> it is safe to reuse the connectiion.
>> If the server fails to send it, then it is broken, and so the failed
>> samples are to be expected.
>>
>
> I think we need to make something at least for servers like Amazon S3 which
> close connections after number of uses.
> Did you check to see if this kind of server send a keep alive header ?

I just tested again with jmeter.a.o.
It returns headers of the form:

Keep-Alive: timeout=5, max=100
Connection: Keep-Alive
...
Keep-Alive: timeout=5, max=99
Connection: Keep-Alive
...
etc
...
Keep-Alive: timeout=5, max=1
Connection: Keep-Alive
...
Connection: close

So the HC connection manager does not need to keep track of the
remaining re-use count; the server disconnects at the end of the last
request.
Nice and simple.

I assume S3 does the same as jmeter.a.o if it is well-behaved.

> Anyway on my side I think what has been changed in 2.11 should not be
> reverted, because for servers correctly configured you don't get these
> errors, I made 3 campaigns on different servers  with 2.11 and never got
> this kind of issues.

Agreed, no need to revert.

> But maybe we should document it better somewhere.

Yes, the error and likely cause should be documented.
Probably easiest to start as a Wiki page.

>
>
> --
> Cordialement.
> Philippe Mouawad.

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