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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 Thu, 18 Aug 2011 19:13:05 GMT
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.
b. In Axis2 <= 1.5, Keep-Alive connections will always be leaked
unless one configures a custom connection manager. 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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