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From Andreas Veithen <andreas.veit...@gmail.com>
Subject Re: how to avoid CLOSE_WAITs without the use of the REUSE_HTTP_CLIENT option?
Date Fri, 19 Aug 2011 18:31:38 GMT
On Fri, Aug 19, 2011 at 11:44, Amila Suriarachchi
<amilasuriarachchi@gmail.com> wrote:
>
>
> On Fri, Aug 19, 2011 at 12:43 AM, Andreas Veithen
> <andreas.veithen@gmail.com> wrote:
>>
>> Although the practical conclusions of that blog post are correct, the
>> explanation is nevertheless based on a misunderstanding of what the
>> actual issue is. Quoting from the article:
>>
>> "idea behind recent change in axis2 is to use connection pool facility
>> of MTHCM to avoid new http connection every time you call webservice"
>>
>> "So if we are using axis2 1.5.1 onwards we need to release the
>> connection to the pool since we can not have more than one MTHCM"
>>
>> This is not entirely wrong, but it is still incomplete. The problem in
>> Axis2 versions before 1.5.1 was that in addition to creating a new
>> connection for every request, the HTTP transport was unable to ensure
>> that these connections are properly closed. This caused the CLOSE_WAIT
>> problem mentioned by Himakar.
>>
>> Another consequence of this bug was that for these versions of the
>> HTTP transport, it didn't really matter whether the application code
>> invoked ServiceClient#cleanupTransport() or not. There was a
>> connection leak anyway. In many cases this actually didn't cause an
>> incident because the connections would eventually be closed by the
>> garbage collector. The consequence of this is that there is lot of
>> application code written for Axis2 versions before 1.5.1 that fails to
>> call cleanupTransport() in the appropriate places.
>>
>> The connection leak was finally fixed in Axis2 1.5.1 (kudos to Glen)
>> and the HTTP transport now manages the connections properly. However,
>> the cleanup code relies on the assumption that the application code
>> uses the ServiceClient API properly, and in particular calls
>> cleanupTransport where necessary. If the code fails to do that, then
>> the connection pool used by the HTTP transport will quickly be
>> starved, resulting in a "Timeout waiting for connection" error.
>>
>> To summarize: application code that triggers a "Timeout waiting for
>> connection" with Axis2 >= 1.5.1 was already incorrect in previous
>> versions of Axis2, but the symptoms caused by this incorrect code are
>> different.
>>
>> With this knowledge, it is possible to give an answer to Himakar's
>> original question:
>>
>> a. In Axis2 >= 1.5.1, the CLOSE_WAIT issue never occurs and it is in
>> general not necessary to configure a custom connection manager or
>> HttpClient.
>
> Now the error is Timeout since default connection manager is only allow 2
> connections. I think this can be improved by initiating the connection
> manager at the transport initialization time and having parameters to define
> those at the axis2.xml transport sender level.
>
> The bottom line is still it does not fix the connection related problem out
> of the box. Users have to use the service Client API properly by calling the
> cleanUp transport.
>
>>
>> b. In Axis2 <= 1.5, Keep-Alive connections will always be leaked
>> unless one configures a custom connection manager.
>
> There is no connection leak in the earlier version. But what happen is it
> takes 30 seconds to close the connection.

That is only true if the connection is properly released, in which
case you won't get a "Timeout waiting for connection" error with Axis2
>= 1.5.1. As I said earlier, code that in Axis2 >= 1.5.1 produces a
"Timeout waiting for connection" error will leak connections in Axis2
< 1.5.1, and these connections are not closed after 30 seconds, but
when the garbage collector destroys the connection and the associated
connection pool. If the peer closes the connection before that, then
it will be in state CLOSE_WAIT.

> if the load is high this cause a
> CLOSE_WAIT sate connection accumulation.

If the connection is closed after 30 seconds, then this will primarily
result in connections in state TIME_WAIT, as described in AXIS2-2931.
Connections in state CLOSE_WAIT will only appear if the peer decides
to close them before the 30s timeout.

The TCP state diagram helps to understand this:

http://tangentsoft.net/wskfaq/articles/bitmaps/state-diagram-small.gif

> thanks,
> Amila.
>
>>
>> Another option may
>> be to disable Keep-Alive or switch to HTTP/1.0. In that case it is
>> likely that the call to cleanupTransport() will actually close the
>> connection (to be tested!).
>>
>> Andreas
>>
>> On Thu, Aug 18, 2011 at 07:02, shivendra tripathi <shivendra2u@gmail.com>
>> wrote:
>> > Hope below link would be helpful
>> >
>> > http://shivendra-tripathi.blogspot.com/2011/05/http-transport-in-axis2-how-to-fix.html
>> >
>> > On Thu, Aug 18, 2011 at 3:13 AM, Himakar Chennapragada
>> > <himakar@us.ibm.com>
>> > wrote:
>> >>
>> >> Is there a way to prevent/avoid or minimize the CLOSE_WAITs from
>> >> happening
>> >> when we DO NOT use the REUSE_HTTP_CLIENT option on the ServiceClient
>> >> interface.
>> >>
>> >> We have multiple threads calling out to same or different web services.
>> >>  We use a new ServiceClient for each invocation to an external web
>> >> service
>> >> (same or different service) without the REUSE_HTTP_CLIENT option and
>> >> that
>> >> produces multiple CLOSE_WAITs that seem to grow over time.  We do
>> >> understand
>> >> that using the REUSE_HTTP_CLIENT option helps in this area but we want
>> >> to
>> >> explore other ways without using this option if any.
>> >>
>> >> Best Regards,
>> >> -Himakar
>> >
>> >
>>
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>>
>
>
>
> --
> Amila Suriarachchi
> WSO2 Inc.
> blog: http://amilachinthaka.blogspot.com/
>

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