I am considering using AppEngine for deploying a webapp which I am
developing. As part of my investigation into the AppEngine platform I
have been checking the response time for simple requests. To this end,
I have written a simple PING servlet:
@SuppressWarnings("serial")
public class Ping extends HttpServlet
{
@Override
public void doGet(@SuppressWarnings("unused") HttpServletRequest xiReq,
HttpServletResponse xiResp)
throws IOException
{
xiResp.setContentType("text/plain");
xiResp.getWriter().println("PONG");
}
}
I have then written a java program to make a request every second to
this servlet and time how long it takes to complete the request.
Fetching the page content uses the following code.
private static String getPageContent(String url) throws IOException {
String result = null;
InputStream webStream = new URL(url).openStream();
BufferedReader reader = new BufferedReader(new
InputStreamReader(webStream));
result = reader.readLine();
reader.close();
return result;
}
Every 3 minutes my monitor script outputs data in the following format:
date,num_reqs,num_failedreqs,avg_reqtime,num_normreqs,avg_normreqtime,num_latereqs,avg_latereqtime
normrequests are all requests which take less than 500ms to complete
latereqs are all requests which take longer than 500ms to complete
failreqs are any which throw an IO exception during the download or if
the content received is not equal to "PONG"
My output for the last ~20 minutes is as follows.
Thu Nov 25 10:04:01 GMT 2010,300,0,186,295,171,5,1093
Thu Nov 25 10:09:28 GMT 2010,300,0,191,292,173,8,842
Thu Nov 25 10:14:52 GMT 2010,300,0,184,295,167,5,1177
Thu Nov 25 10:20:15 GMT 2010,300,0,182,294,168,6,876
Thu Nov 25 10:25:46 GMT 2010,300,0,172,298,167,2,827
This shows that in each 5 minute period there are between 2 and
8 "late" requests taking an average of between 827 and 1177ms to
complete.
This compares with the following output from the same period running
against the same servlet on a micro instance running on Amazon EC2.
Thu Nov 25 10:03:53 GMT 2010,300,0,177,300,177,0,0
Thu Nov 25 10:09:20 GMT 2010,300,0,179,299,178,1,583
Thu Nov 25 10:14:43 GMT 2010,300,0,176,299,175,1,545
Thu Nov 25 10:20:07 GMT 2010,300,0,176,299,175,1,531
Thu Nov 25 10:25:37 GMT 2010,300,0,181,298,178,2,669
This shows far fewer "late" requests and the response time for these
slow requests is much lower.
I am making my requests from a server based in the UK. My Amazon EC2
instance is running in "US East". I don't know where Google is running
my AppEngine instance.
Can I do anything to improve the consistency of AppEngine response
times or is the variance I am seeing normal for AppEngine?
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