Coyote Point Systems Equalizer Installation And Administration Manual page 76

Chapter 5: Administering Virtual Clusters
5. Specify the Load Balancing Responsiveness. This value controls how aggressively
Equalizer adjusts the servers' dynamic weights. There are three responsiveness
settings: Slow, Medium and Fast. This value affects the dynamic weight spread,
weight spread coefficient, and optimization threshold used by Equalizer when it
performs adaptive load balancing:
66
Adaptive—This is the default load balancing policy. Equalizer monitors the
following performance indicators for each server and balances the load
accordingly:
Server response time—how long it takes the server to begin sending reply
packets after it receives a request.
Active connection count—the number of connections currently active on the
server.
Server agent value—the value returned by the server agent daemon running on
the server.
Fastest Response—the highest percentage of requests is dispatched to the server
with the shortest response time. This is done carefully because if too many
requests are dispatched to a server it can become overloaded and its response
time will increase. The policy optimizes the cluster-wide response time.
The number of active connections and server agent values (if configured) are still
taken into account. Even if the response time on a server is small (meaning that
the server is the fastest in the cluster), if the server's active connection count and
server agent values are high, Equalizer might not dispatch new requests to the
server.
Least Connections—the highest percentage of requests is dispatched to the
server with the smallest number of active connections. Like with the fastest
response option, the server's response time and server agent value are still taken
into account so that the server is not overloaded.
Server Agent—the highest percentage of requests is dispatched to the server
with the lowest server agent value. Other server values such as the number of
connections and response time are also taken into account to avoid overloading
the server.
Dynamic Weight Spread—how far a server's dynamic weight can vary from its
static weight. The spread is expressed as a percentage. For example, if the spread
is 40% and the server's static weight is 100, Equalizer will not change the server's
dynamic weight to more than 140 or less than 60.
The responsiveness settings correspond to the following dynamic weight
spreads:
Slow: 20% (dynamic weight changes are limited)
Medium: 40% (normal)
Fast: 60% (dynamic weight changes are very flexible)
Weight Spread Coefficient—regulates changes to a server's dynamic weight.
The coefficient is expressed as a percentage of the server's static weight. A slower
weight spread coefficient is going to cause dynamic weight changes to occur
more slowly as the dynamic weight's deviation from the server's static weight
increases. For example, if the server's static weight is 100 and its dynamic weight
Equalizer Installation and Administration Guide