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From "Sebb (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HTTPCORE-254) Erratic results from metrics
Date Thu, 14 Apr 2011 10:56:06 GMT
Erratic results from metrics
----------------------------

                 Key: HTTPCORE-254
                 URL: https://issues.apache.org/jira/browse/HTTPCORE-254
             Project: HttpComponents HttpCore
          Issue Type: Bug
    Affects Versions: 4.1
            Reporter: Sebb


The values obtained from getMetrics are erratic. For example, the following code:

DefaultHttpClient httpclient = new DefaultHttpClient();
try {
    HttpRequestBase req = new HttpGet("http://wiki.apache.org/jakarta-jmeter/JMeterCommitters");
    for(int i = 0; i<3;i++) {
            HttpContext localContext = new BasicHttpContext();
            HttpResponse rsp = httpclient.execute(req, localContext);
            System.out.println(rsp.getStatusLine());
            HttpConnection conn = (HttpConnection) localContext.getAttribute(ExecutionContext.HTTP_CONNECTION);
            HttpConnectionMetrics metrics = conn.getMetrics();
            long hdr = metrics.getReceivedBytesCount();
            System.out.println("hdr "+hdr);

            HttpEntity entity = rsp.getEntity();
//            Thread.sleep(1500);
            if (entity != null) {
                EntityUtils.consume(entity);
            }
            long total = metrics.getReceivedBytesCount();
            System.out.println("tot "+total);
            metrics.reset();
        }
    } finally {
            // When HttpClient instance is no longer needed,
            // shut down the connection manager to ensure
            // immediate deallocation of all system resources
            httpclient.getConnectionManager().shutdown();
    }
}

May produce:

HTTP/1.1 200 OK
hdr 284
tot 566
HTTP/1.1 200 OK
hdr 283
tot 313
HTTP/1.1 200 OK
hdr 283
tot 313

Enabling the sleep produces more consistent (but still inaccurate) results:

HTTP/1.1 200 OK
hdr 284
tot 10946
HTTP/1.1 200 OK
hdr 283
tot 10945
HTTP/1.1 200 OK
hdr 283
tot 10945

Rather unexpected behaviour, but as it happens, a very simple cause:

// AbstractSessionInputBuffer lines 184-189
        // If the remaining capacity is big enough, read directly from the
        // underlying input stream bypassing the buffer.
        if (len > this.minChunkLimit) {
            return this.instream.read(b, off, len);
        } else {
            // otherwise read to the buffer first

The code also bypasses the metrics collection...

Fixing this results in the following (with or without the sleep):

{noformat}
HTTP/1.1 200 OK
hdr 284
tot 16643
HTTP/1.1 200 OK
hdr 283
tot 16642
HTTP/1.1 200 OK
hdr 283
tot 16642
{noformat}

[Note that the slight variation in size is due to a minor change in the headers.]

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