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LSAM CONFIGURABLE CACHE REPLACEMENT POLICIES
============================================
Document Version 1.0 (3/25/98)
More Information: http://www.isi.edu/lsam/dynamic-cache

Introduction
------------
The LSAM Proxy suports several different cache replacement algorithms.
The choice of algorithm can be specified in the httpd.conf configuration
file and is static.  This allows the proxy administrator to select
an algorithm appropriate to the use of the server.

The default Apache algorithm replaces files based on their expire
times, the files closest to expiring will be removed first.  The
new algorithms that have been added include:  FIFO, LRU, file
size replacement (replace large or small files first), and download-
time replacement (replace the files with the longest or shortest
download time first).

At present, Apache uses the same algorithm throughout the life
of the server.  In the future, we will implement mechanisms to
allow a new caching algorithm to be selected by the server 
administrator or the server itself at run-time based on usage
observations.

Compilation
-----------
1. Modify apache/src/Configuration to include this line:
   EXTRA_CFLAGS+=-D_LSAM_CACHE

2. Run the Apache configuration utility

3. Compile

Configuration
-------------
To specify the caching algorithm, activate the following directive in the 
httpd.conf file for your proxy server:

   # CacheGCAlgorithm 0

You must also specify which caching algorithm should be used.
The value specified selects an individual algorithm as follows:
   0 = EXPIRE, replaces files based on the oldest expire times
   1 = LARGE, replaces largest files first
   2 = SMALL, replaces smallest files first
   3 = LONG_DL, replaces files with longest download times first
   4 = SHORT_DL, replaces files with shortest download times first
   5 = FIFO, straight FIFO file replacement
   6 = LRU, straight LRU file replacement
Integer values larger than 6 default to EXPIRE, which is the original
Apache replacement algorithm.

Execution
---------
Run the server normally.

Upcoming Features
-----------------
The following features can be expected in the next release of
the LSAM Proxy:

   * Cache replacement algorithm can be changed without restarting
     the proxy
	
   * Mechanisms will be in place to collect data about the usage
     of the cache and server as support for a future