Perlbal::Manual::FailOver(3pm) User Contributed Perl Documentation Perlbal::Manual::FailOver(3pm)NAME
Perlbal::Manual::FailOver - Fail Over mechanism in Perlbal
VERSION
Perlbal 1.78.
DESCRIPTION
How Perlbal's Fail Over mechanism works.
Fail Over
Whenever Perlbal fails to open a connection to a machine, it assumes that machine is not available and spreads the load between the
remaining servers. It keeps trying to open connections to that server according to "error_retry_schedule".
If there are no available servers, Perlbal will keep trying to open connections to the servers until "idle_timeout" is reached, upon which
it will close the connection to the user. Clients interpret that closing differently: most will assume a 500 HTTP code, a few assume a 200
OK with empty content.
For more information on parameters "idle_timeout" and "error_retry_schedule" see Perlbal::Manual::ReverseProxy.
SEE ALSO
Perlbal::Manual::LoadBalancer, Perlbal::Manual::ReverseProxy.
perl v5.14.2 2011-01-23 Perlbal::Manual::FailOver(3pm)
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Perlbal::Manual::HighPriority(3pm) User Contributed Perl Documentation Perlbal::Manual::HighPriority(3pm)NAME
Perlbal::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(3pm)