Installing and Configuring HP WebQoS Peak on Linux

26 Chapter3
HP WebQoS Peak on Linux for the Apache Web Server
Configuring WebQoS Peak on Linux for Apache
System Resources Sharing Among Virtual Hosts
By default, each virtual host equally shares the system resources.
However, this does not guarantee equal use of the resources. Virtual
hosts hosting active sites may use more than their fair share of system
resources, at the expense of other virtual hosts. A more equitable use of
system resources can be achieved using one of the techniques described
below.
You can influence the access of virtual servers to system resources by
using different load thresholds for the virtual hosts. For instance, you
could set the load threshold lower for virtual hosts that have a tendency
to use most of the system resources. Conversely, you can set the load
threshold higher, or even turn off admission control, for virtual hosts
that have little impact on the system resources.
You can use the HPACShareUnits directive to give more weight to some of
the virtual hosts. The default for this directive is “1.” For example, to give
more weight to some of the virtual hosts, use the following directive in
your configuration file:
HPACShareUnits 2
To understand the effect of this command, assume that you have three
virtual hosts, A, B and C: A is assigned one share of system resources, B
is assigned two shares and C is assigned three shares. (There are a total
of six shares.) This amounts to assigning 17% of system resources to A
(1 / 6 * 1), 33% to B (1 / 6 * 2) and 50% to C (1 / 6 * 3).
The assigned share of system resources is used to compute the actual
priority threshold for each virtual host from the server-wide priority
threshold. You can set the value for the server-wide priority threshold
with HPACAdmitPriorityThreshold. The default for this directive is
“0.9.”. For example, to set the server-wide priority threshold to .75, use
the following directive in your configuration file:
HPACAdmitPriorityThreshold 0.75
The setting above will allow up to 75% of all sessions to be priority
sessions. Beyond this threshold, even priority sessions are rejected. The
value set with directive is used to compute the priority threshold for
individual hosts, taking into account the assigned share (see
HPACShareUnits above).
The assigned share is also used to give priority to under-represented
virtual hosts, when virtual host isolation is in effect. Virtual host