DavisSim: Another Web Cache Simulator

>>> Under construction. <<<

The purpose of DavisSim was to provide a method by which the performance of customized web policies could be evaulated for the web. DavisSim utilizes as input a file that lists scripts that can be used to customize the web caching policies. It then uses these scripts in conjuction with a trace of web accesses.
DavisSim is based on the design of the Wisconsin Web Cache simulator. Both simulators are written for non-uniform size web document caches. DavisSim differs in that although the initial design was based on the Wisconsin Web Cache Simulator, it has been rewritten in C++. Additionally, DavisSim supports different techniques for describing coherency and additionally measures true/false hits and true/false misses.

Design

DavisSim uses a pre-processed web trace. This web trace contains the time of request and server, document and client identifiers (see the next section.) Each request in the trace causes either a New-Store event if an object is not already in the cache, or an Access-Inline event if the object is cached. We do not support Routing events at this time because DavisSim does not simulate cooperative caching.
The cache operations allow scripts to store objects in the cache and purge objects to make more space. Internally the simulator maintains statistics about true/false hits, true/false misses, and latencies. A true hit occurs when the object being requested hits in the cache and the object has not been modified from the version stored in the cache. If the object was modified it is considered a false hit. Similarly, if an IMS request is generated and the object has been modified we refer to this as a true miss, otherwise a false miss.

Use

davisSim [opts]*, where opts =

--size n, set the cache size to n, default 4Meg
--root dir, prefix to apply to script lookups, default ./
--config file, specifies CacheL configuration script, default script.rc
--init file, specifies initialization script to run, default none
--cleanup file, specifies script to run at finish, default none
--in file, specifies data file to read, ucd format, default stdin
--out file, specifies where to write output, default stdout
--debug opts, specifies debug levels desired, default 10=5,81=2,1=5,12=5

Input Data format used by DavisSim

The trace file format consists of the following seven integer numbers:

Unique Server ID
Unique Page ID on that server
Size of file requested
Elapsed time required to retrieve file
Last modification time
Time of access
Unique Client I

TarBall

DavisSim has been written and used on Linux 2.0 and 2.2 kernels. There is no reason that it would not run on other versions of UNIX. The source code is available here. I think that I use several different personal libraries, which will be placed on this web page soon. EMAIL Fritz, barnes@cs.ucdavis.edu, if the libraries are not already on the web page.

DavisSim Source
Libraries
DavisSim Linux Executable

J. Fritz Barnes