Specifications

Working with Virtual Clusters
Equalizer Installation and Administration Guide 75
server, and so on. When Equalizer reaches the last server, it repeats the cycle. If a server in the
cluster is down, Equalizer does not send requests to that server. This is the default method.
The round robin method does not support Equalizer’s adaptive load balancing feature; so,
Equalizer ignores the servers’ static weights and does not attempt to dynamically adjust server
weights based on server performance.
• static weight load balancing distributes requests among the servers depending on their static
weights. A server with a higher static weight gets a higher percentage of the incoming
requests. Think of this method as a weighted round robin implementation. Static weight load
balancing does not support Equalizer’s adaptive load balancing feature; Equalizer does not
dynamically adjust server weights based on server performance.
• adaptive load balancing distributes the load according to the following performance
indicators for each server.
Server response time is the length of time for the server to begin sending reply packets
after Equalizer sends a request.
Active connection count shows the number of connections currently active on the server.
Server agent value is the value returned by the server agent daemon running on the
server.
• fastest response load balancing dispatches the highest percentage of requests to the server
with the shortest response time. Equalizer does this carefully: if Equalizer sends too many
requests to a server, the result can be an overloaded server with slower response time. The
Fastest Response policy optimizes the cluster-wide response time.
Under Fastest Response, Equalizer checks the number of active connections and server agent
values (if configured); but both of these have less of an influence than they do under adaptive
load balancing. Even if a server’s response time is the fastest in the cluster but its active
connection count and server agent values are high, Equalizer might not dispatch new requests
to that server.
• least connections load balancing dispatches the highest percentage of requests to the server
with the least number of active connections. In the same way as Fastest Response, Equalizer
tries to avoid overloading the server so it checks the server’s response time and server agent
value. Least Connections optimizes the balance of connections to servers in the cluster.
• server agent load balancing dispatches the highest percentage of requests to the server with
the lowest server agent value. In a similar way to Fastest Response, Equalizer tries to avoid
overloading the server by checking the number of connections and response time. This
method only works if server agents are enabled. For more information about server agents,
see “Configuring a Cluster to Use Server Agents” on page 78.
Equalizer’s Load Balancing Response Settings
The responsiveness setting controls how aggressively Equalizer adjusts the servers’ dynamic
weights. Equalizer provides five response settings: Slowest, Slow, Medium, Fast, and Fastest. The
response setting affects the dynamic weight spread, weight spread coefficient, and optimization
threshold that Equalizer uses when it performs adaptive load balancing:
• Dynamic Weight Spread indicates how far a server’s dynamic weight can vary (or spread)
from its static weight.