Perlbal::Manual::HighPUseriContributed Perl DoPerlbal::Manual::HighPriority(3)NAMEPerlbal::Manual::HighPriority - Perlbal's high/low priority queueing
system.
VERSION
Perlbal 1.78.
DESCRIPTION
This document describes Perlbal's high/low priority queueing system.
Queuing system
Perlbal has three queues: normal, high priority and low priority.
As their names suggest, this means that usually requests get to the
normal queue and are dispatched in FIFO order, with high priority
requests going to a different queue that gets ahead of the normal one
and a low priority queue that only gets done when the high and normal
queues are empty.
In a nutshell, whenever Perlbal needs to select which request to take
care of next, it first looks for requests in the high priority queue;
if that one is empty, it then looks into the normal queue; and, if the
normal queue is empty too, it finally looks in the low priority queue.
High priority with cookies
Perlbal can use cookies to determine if a request should go to the high
priority queue (configurable).
The parameters to configure this are "high_priority_cookie" and
"high_priority_cookie_contents"; the first defines the name of the
field to check for on the cookie and the second one defines the content
in that field that will trigger the request going to the fast queue:
SET myservice.high_priority_cookie = name_of_the_field
SET myservice.high_priority_cookie_contents = required_content_on_that_field
Here's a clearer example:
SET myservice.high_priority_cookie = highpriority
SET myservice.high_priority_cookie_contents = yes
High priority with plugins
The plugin Perlbal::Plugin::Highpri supports making requests high
priority by URI or Host. Also check "make_high_priority" under
Perlbal::Manual::Hooks.
Queue relief
Sometimes if the high priority queue is really busy, the standard queue
will suffer from resource starvation. The queue relief system helps
prevent this. When there are "queue_relief_size" or more connections in
the standard queue, newly available backends have a
"queue_relief_chance" percent chance of taking a request from the
standard priority queue instead of the high priority queue.
SET web_proxy.queue_relief_size = 2000
SET web_proxy.queue_relief_chance = 30 # 0-100, in percent
SEE ALSO
"make_high_priority" and "make_low_priority" in Perlbal::Manual::Hooks,
Perlbal::Plugin::HighPriority.
perl v5.14.2 2011-01-23 Perlbal::Manual::HighPriority(3)
