Record only a fraction of all requests with AppStats for App Engine in Java

Question

We're trying to reduce the overhead of AppStats on a high traffic website. AppStats for Python has a configuration setting appstats_RECORD_FRACTION which limits the number of requests that are recorded. This allow you to record the stats for only a small percentage of all request, e.g. 1%.

I cannot find any reference in the documentation for a similar configuration setting for AppStats for Java. Does anyone know how to configure this?

Answer 1

It seems that after years there still isn't support for "Record Fraction" in appstats for Java. The workaround I found for it was implementing a custom filter:

package com.example.server.servlet;

import com.google.appengine.tools.appstats.AppstatsFilter;

import java.io.IOException;
import java.util.Random;

import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

public class AppstatsImprovedFilter extends AppstatsFilter {

    private double recordFraction;
    private Random random;

    @Override
    public synchronized void init(FilterConfig config) {
        super.init(config);
        String recordFractionConfig = config.getInitParameter("recordFraction");
        recordFraction = recordFractionConfig == null ? 1.0 : Double.parseDouble(recordFractionConfig);
        random = new Random();
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain filters)
            throws IOException, ServletException {
        if (recordFraction < 1.0 && random.nextDouble() > recordFraction) {
            filters.doFilter(request, response);
        } else {
            super.doFilter(request, response, filters);
        }
    }
}

Then you use this filter instead of AppstatsFilter one in web.xml:

<filter>
    <filter-name>appstats</filter-name>
    <filter-class>com.example.server.servlet.AppstatsImprovedFilter</filter-class>
    <init-param>
        <param-name>calculateRpcCosts</param-name>
        <param-value>true</param-value>
    </init-param>
    <init-param>
        <param-name>recordFraction</param-name>
        <param-value>0.05</param-value>
    </init-param>
</filter>