Discrete Event Simulation of a Web Server assuming closed system

A python implementation of simulation of a closed loop web server with context switches and timeouts.

Features

• Multi-core and multi threaded server machine
• Round robin & First come first serve (FCFS) policies for scheduling accounting context switch overhead
• Users are in a standard closed loop - issue request, wait for response, think then issue request again.
• Options of having deterministic, exponential, uniform and constant+exponential distribution for think time, service time and timeout
• Request Timeouts are implemented in two ways
  • TimeoutAtWriting, where server gets to know that timeout has happened only at the time of writing results to socket.
  • TimeoutBeforeWriting, where server proactively checks for timeout at the beginning of every slot provided to that request.

Metrics being collected (averages)

• Response time
• Number of users in system
• Utilization
• Throughput
• Goodput
• Badput
• Request drop rate
• Context switched per request

Dependencies

• Make sure you have python3.5 & pip3 installed Install these dependencies
• statistics pip3 install statistics
• matplotlib pip3 install matplotlib
• yaml pip3 install pyyaml If you get environment error, then use pip3 install pyyaml --user and similarly for other dependencies.

Instructions to run

1. There are two folders in directory Code, TimeoutAtWriting and TimeoutBeforeWriting containing their respective codes as mentioned above.
2. Change directory to one of these and then:
   • If you want to change the configuration of the system, make changes in config.yaml
   • python3 main.py <num_users> <result_file> <log_needed> e.g., python3 main.py 1500 results.txt 0.
   • Otherwise, If you want to generate plots by varying number of users, then
     • Run python3 overall_script.py (You may want to change the number of users in the array users in overall_script.py). It will take around 2 minutes to run and will save all plots in folder Results

Few Plots

TODO

1. Use Welch’s procedure to discard transient phase instead of current ad-hoc choice.
2. Add more realistic features to the system like I/O.