Coyote Point Systems Equalizer, Installation And Administration Manual

Page: 54 / 144

Chapter 4:Administering Equalizer Operation
44 Equalizer Installation and Administration Guide
■
Service time —the time it takes a server to start sending reply packets once a client
request has been received. This value is very small for servers that are primarily
serving static html pages—typically 100-200 milliseconds. If the server is serving a lot
of active pages and cgi-bins, this value will be much higher. The service time increases
when the server is under heavy load because client requests are queued until the
server can handle them.
■
Computed load —a measure of the performance of the server relative to the overall
performance of the cluster. Equalizer tries to normalize the cluster-wide computed
load value to 100. If the server’s computed load value is above 100, it is performing
below the overall cluster performance.
A server’s computed load value is derived from its service time, number of active
connections, and server agent value (if configured). It is also takes into account the
load balancing policy used by the cluster.
Ideally, a server’s computed load should be around 100, though values in the range
85-115 are reasonable. If the server’s computed load is higher than 115, the server is
not performing well. If adaptive load balancing is being used, Equalizer will lower the
server’s dynamic weight to reduce the number of connections sent to that server. If the
server’s computed load value is less than 85, the server is performing very well and
Equalizer will attempt to improve cluster-wide performance by increasing the server’s
dynamic weight to direct more traffic to it. Such adjustments to the server’s weight
will in turn affect its computed load value.
■
Dynamic weight —the percentage of incoming traffic that is being dispatched to this
server. For example, if there are three servers in the cluster with dynamic weights of
100, 80, and 120, the first server will get 100/(100+80+120) or 33.3% of the incoming
traffic.
If a server is down, its dynamic weight is zero. If a server crashes and reboots, the
period that the server was down shows up as a gap in the dynamic weight plot.
If you are not using adaptive load balancing (the load balancing policy is set to round
robin or static weight), dynamic weights are not used. See “Configuring a Cluster’s
Load-Balancing Options” on page 64 for more information about setting the load
balancing policy and adaptive load balancing.
■
Server agent —the value returned by the server agent daemon. When queried, the
server agent returns a value in the range 0-100. If the cluster is not configured to use
the server agent or the server agent daemon is not running on this server, the server
agent value defaults to 50.
Server agent values above 60-70 indicate that the server is overloaded. If this persists
and adaptive load balancing is enabled, Equalizer will respond by reducing the
server’s dynamic weight so that fewer requests will be routed to the server.
Note – If all of your servers have server agent values above 70, you probably have more traffic
than your servers can handle efficiently. In this case, Equalizer can help by intelligently managing
the overload, but the long-term solution is to upgrade the servers or add new ones.