Hi,
we've developped a web application performance tool. Our product intensivly
uses httpclient (currently 3.1) to measure response time of these web
applications (single url or sequence of url to copy a human being navigation).
The main principle of our tool is to perform the same requests at a fixed
frequency (5 minutes most of the times) to be able to compute Service Level
Agreements.
We've detected some "strange" behaviours on some monitors (=sequence of url
request retreived with httpclient). Sometimes (1% of the executions), some
requests take more time (like 3 sec instead of 100ms) to be performed.
We cannot say for sure for the moment that the network elements of the
architecture are not concerned but let's assume first that our problems are not
network related (and I'm not saying that the guilty part is httpclient ;], if
you can help me to find the proof that it's network related, let's go!)
Logs have been added on the web server side (apache) using a %D in the
LogFormat specification. The response times measured on apache side don't match
the ones we get using httpclient, not even closer (we see 3 seconds on
httpclient side, we see less that 1 ms on apache side).
We've traced the httpclient call and we've been able to detect 2 different
behaviours:
the first one occurs during the connection opening, inside
HttpConnection.open() call. I've added the "OPENED" trace that comes just after
the isOpen=true.
=============================
isOpen = true;
if (LOG.isDebugEnabled()) {
LOG.debug("connection to " + host + ":" + port + "
OPENED");
}
=============================
our logs:
==============================
[DEBUG] [22/10/08 12:38:26.250] [httpclient.HttpConnection]<7747> Open
connection to 160.92.110.240:443 (HttpConnection.java:717)
[DEBUG] [22/10/08 12:38:29.246] [httpclient.HttpConnection]<7747> connection to
160.92.110.240:443OPENED (HttpConnection.java:771)
==============================
I'm aware that there can be a lot of reason why the HttpConnection.open() lasts
so long, but does it exist explanation NOT related to network only issues?
the second one occurs during the flush of the request OutputStream
==============================
[DEBUG] [22/10/08 14:00:26.234] [httpclient.HttpConnection]<16536> enter
HttpConnection.flushRequestOutputStream() (HttpConnection.java:851)
[DEBUG] [22/10/08 14:00:29.240] [httpclient.HttpConnection]<16536> leaving
HttpConnection.flushRequestOutputStream() (HttpConnection.java:854)
==============================
my modifications are:
==============================
public void flushRequestOutputStream() throws IOException {
LOG.trace("enter HttpConnection.flushRequestOutputStream()");
assertOpen();
outputStream.flush();
LOG.trace("leaving HttpConnection.flushRequestOutputStream()");
}
==============================
what can explain such a long time to flush the request OutputStream?
Am I wrong or does this output stream only "contains" the request built by
httpclient? That would mean that the web server is taking a (too) long time to
accept the request?
some more details: we have these behaviours using different hosts for our
performance tool, so we can assume that these response times are not related to
the load of the host that is running the httpclient.
Thanks for reading :)
Christophe
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