perlbal::manual::highpriority(3pm) [debian man page]

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)

Perlbal::FAQ(3pm)					User Contributed Perl Documentation					 Perlbal::FAQ(3pm)

NAME

       Perlbal::FAQ - Frequently Asked Questions about Perlbal

   VERSION
       Perlbal 1.78.

   DESCRIPTION
       This document aims at listing several Frequently Asked Questions regarding Perlbal.

   Configuring Perlbal
       Is there a sample "perlbal.*" I can use for my "init.d"?

       Yes, you can find one under "debian/perlbal.init". It implements "start", "stop" and "restart/force-reload". Make sure you adjust it to
       your particular taste and/or needs.

       Is there a way to make perlbal re-read the config file without shuting it down?

       No, there is not. But typically, if you're making changes, you can just make them on the management console, which doesn't require any
       restart whatsoever.

       Still, restarting is probably easy. The trick to it is to simulate a graceful restart.

       How can I implement a graceful restart?

       Here's a sample script that will allow you to perform a graceful restart:

	   $ cat restart-perlbal.sh
	   echo "shutdown graceful" | nc localhost 60000
	   /usr/local/bin/perlbal --conf=/etc/perlbal.conf

       The idea is that you tell the old Perlbal to do a graceful shutdown; that immediately closes all of the listening sockets, so new
       connections are not accepted. As soon as that's done (which is instant) you can start up a new Perlbal.

       This gives you a minimum of downtime that can be measured on the order of milliseconds (the time it takes for the new Perlbal to start up).

       Remember that you need to have a "management" service listening on port 60000 for this example to work. See Perlbal::Manual::Management.

   Load Balancing
       What balancing algorithm does Perlbal use?

       Currently, Perlbal supports only one balancing method: "random".

	   SET pool balance_method = 'random'

       With this mode, Perlbal selects one of the nodes within the pool randomly for each request received. It prefers reusing existing idle
       backend connections if backend_persist is enabled, which is faster than waiting for a new connection to open each time.

   Plugins
       Can I influence the order plugins are used?

       Yes. When you set the plugins for your service they get to register their hooks in order.

	   SET plugins = AccessControl HighPri

       These hooks are pushed into an array, which means that they preserve the order of the plugins.

   HTTP, SSL
       Does perlbal support HTTP 1.1?

       Perlbal for the most part only speaks HTTP/1.0 both to clients and to backend webservers. It happily takes requests advertising HTTP/1.1
       and downgrading them to HTTP/1.0 when speaking to backend serves.

       It knows all about persistent connections (in both 1.0 and 1.1) and will reply with HTTP/1.0 Connection: keep-alive the request was only
       implicitly keep-alive with HTTP/1.1.  etc.

       Perlbal is now also starting to speak more of 1.1. For instance, Perlbal does support receiving transfer-encoding "chunked" requests from
       clients (a feature of HTTP/1.1), will send a "100 Continue" in response to "Expect: 100-continue", and will parse the chunked requests,
       writing the request-of-unknown-length to disk (only if "buffered_uploads" is enabled), and then will send an HTTP/1.0 request to the
       backends, with the actual "Content-Length" (now known) filled in.

       When more of 1.1 is supported, it will become an option, and later become the default. However, after several years of usage, there just
       hasn't been that much of a reason. The chunked requests (common from mobile phones uploading large images) has been the most annoying
       shortcoming but now that it's solved, it's questionable whether or not more of HTTP/1.1 will be supported.

       Does perlbal support SSL?

       Yes. To use SSL mode you'll need IO::Socket::SSL "v0.98+" installed.

       You can do SSL either on "web_server", "reverse_proxy" or "selector" modes, but not on a vhost-based "selector" service, because SSL and
       vhosts aren't compatible.

       See the configuration file ssl.conf under conf/ for an example.

   SEE ALSO
       Perlbal::Manual.

perl v5.14.2							    2012-02-20							 Perlbal::FAQ(3pm)