Sliding Window Counter 2 (Java)

Marc J. Greenberg <codemarc@gmail.com>

This is a counter which keeps track of the number of events have occurred in a given window of time. An event is a stateless record of occurrance at a given moment in time. Sliding windows have a fixed known size. We want to know how many events have occurred in:

Window	Scope	Size
Last second	millisecond	1000
Last minute	second	60
Last hour	minutes	60

This illustration is taken from eep-js

Sliding window of size 2 ticks computing, counting occurances.

     t0     t1      (emit)   t2             (emit)       tN
   +---+  +---+---+          -...-...-
   | 4 |  | 2 | 4 |   <6>    : x : x :
   +---+  +---+---+          _...+---+---+               ...
              | 2 |              | 2 | 1 |    <3>
              +---+              +---+---+
                                     | 2 |
                                     +---+

Build

To build Sliding Window Counter 2 locally you need:

• Java SE Development Kit 8 docs.oracle.com
• maven 3.3.9 maven.apache.org

After you install the pre-reqs and clone the repository you can:

command	action
mvn package	create artifacts ready to test
mvn clean	remove build files
mvn eclipse:eclipse	create a eclipse project files and dependencies
mvn eclipse:clean	remove eclipse project files

Implememtation

I am using restx as a framework to host a webapp and a rest based api that exposes the sliding window counter functionality. The framework allows me to document my api and provide a quick way to test it. Once you have a running version of the app you can Login to the LOCAL RESTX Admin console using the credentials admin / codemarc. From the console you can test the various api calls.

Try it

For your convenience I am hosting a container based version of this app on my site.
Login to the RESTX Admin console
or simply hit my api endpoints: http://codemarc.net:8080/api

• http://codemarc.net:8080/api/v1/increment
• http://codemarc.net:8080/api/v1/numLastSecond
• http://codemarc.net:8080/api/v1/numLastMinute
• http://codemarc.net:8080/api/v1/numLastHour
• http://codemarc.net:8080/api/v1/count

Run

After you build the project you can run the server locally it as follows:

$ java -jar jetty-runner.jar target/swc2-1.0.war

Alternatively you of you have docker installed you can:

# build a container 
docker build -t codemarc/swc2 .

# or pull it
$ docker pull codemarc/swc2

# and run it in a container
$ docker run -it -p 8080:8080 --rm codemarc/swc2

Testing

In order to test the functionality you could issue http get requests like

$ curl -X GET http://localhost:8080/api/v1/increment
$ curl -X GET http://localhost:8080/api/v1/increment
$ curl -X GET http://localhost:8080/api/v1/increment

$ curl -X GET http://localhost:8080/api/v1/numLastHour
4

$ curl -X GET http://localhost:8080/api/v1/count
{
  "LastHour": 4,
  "LastMinute": 4,
  "LastSecond": 0
}

Apache Bench

I often use Apache Bench to do some simple benchmarking. The snippet below runs apache bench, 1000 HTTP requests, 10 at a time.

I usually recycle my server before I run this type of test

$ curl -X GET http://localhost:8080/api/v1/count && \
ab -n 1000 -c10 http://localhost:8080/api/v1/increment && \
curl -X GET http://localhost:8080/api/v1/count && \
Sleep 1 && \
curl -X GET http://localhost:8080/api/v1/count 
Sleep 1 && \
curl -X GET http://localhost:8080/api/v1/count 

{
  "LastHour": 0,
  "LastMinute": 0,
  "LastSecond": 0
}
This is ApacheBench, Version 2.3 <$Revision: 1748469 $>
Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Licensed to The Apache Software Foundation, http://www.apache.org/

Benchmarking localhost (be patient)
Completed 100 requests
Completed 200 requests
Completed 300 requests
Completed 400 requests
Completed 500 requests
Completed 600 requests
Completed 700 requests
Completed 800 requests
Completed 900 requests
Completed 1000 requests
Finished 1000 requests


Server Software:        Jetty(7.x.y-SNAPSHOT)
Server Hostname:        localhost
Server Port:            8080

Document Path:          /api/v1/increment
Document Length:        0 bytes

Concurrency Level:      10
Time taken for tests:   0.360 seconds
Complete requests:      1000
Failed requests:        0
Total transferred:      83000 bytes
HTML transferred:       0 bytes
Requests per second:    2778.31 [#/sec] (mean)
Time per request:       3.599 [ms] (mean)
Time per request:       0.360 [ms] (mean, across all concurrent requests)
Transfer rate:          225.20 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        0    1   0.5      1       3
Processing:     1    2   5.4      2      64
Waiting:        0    2   4.9      1      53
Total:          1    3   5.3      3      64

Percentage of the requests served within a certain time (ms)
  50%      3
  66%      3
  75%      3
  80%      4
  90%      4
  95%      5
  98%      5
  99%     52
 100%     64 (longest request)
{
  "LastHour": 1000,
  "LastMinute": 1000,
  "LastSecond": 553
}
{
  "LastHour": 1000,
  "LastMinute": 1000,
  "LastSecond": 210
}
{
  "LastHour": 1000,
  "LastMinute": 1000,
  "LastSecond": 0
}