1Perlbal::Manual::HighPrUisoerritCyo(n3t)ributed Perl DocPuemrelnbtaalt:i:oMnanual::HighPriority(3)
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NAME

6       Perlbal::Manual::HighPriority - Perlbal's high/low priority queueing
7       system.
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9   VERSION
10       Perlbal 1.78.
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12   DESCRIPTION
13       This document describes Perlbal's high/low priority queueing system.
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15       Queuing system
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17       Perlbal has three queues: normal, high priority and low priority.
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19       As their names suggest, this means that usually requests get to the
20       normal queue and are dispatched in FIFO order, with high priority
21       requests going to a different queue that gets ahead of the normal one
22       and a low priority queue that only gets done when the high and normal
23       queues are empty.
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25       In a nutshell, whenever Perlbal needs to select which request to take
26       care of next, it first looks for requests in the high priority queue;
27       if that one is empty, it then looks into the normal queue; and, if the
28       normal queue is empty too, it finally looks in the low priority queue.
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30       High priority with cookies
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32       Perlbal can use cookies to determine if a request should go to the high
33       priority queue (configurable).
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35       The parameters to configure this are "high_priority_cookie" and
36       "high_priority_cookie_contents"; the first defines the name of the
37       field to check for on the cookie and the second one defines the content
38       in that field that will trigger the request going to the fast queue:
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40           SET myservice.high_priority_cookie = name_of_the_field
41           SET myservice.high_priority_cookie_contents = required_content_on_that_field
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43       Here's a clearer example:
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45           SET myservice.high_priority_cookie = highpriority
46           SET myservice.high_priority_cookie_contents = yes
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48       High priority with plugins
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50       The plugin Perlbal::Plugin::Highpri supports making requests high
51       priority by URI or Host. Also check "make_high_priority" under
52       Perlbal::Manual::Hooks.
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54       Queue relief
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56       Sometimes if the high priority queue is really busy, the standard queue
57       will suffer from resource starvation. The queue relief system helps
58       prevent this. When there are "queue_relief_size" or more connections in
59       the standard queue, newly available backends have a
60       "queue_relief_chance" percent chance of taking a request from the
61       standard priority queue instead of the high priority queue.
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63           SET web_proxy.queue_relief_size = 2000
64           SET web_proxy.queue_relief_chance = 30 # 0-100, in percent
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66       SEE ALSO
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68       "make_high_priority" and "make_low_priority" in Perlbal::Manual::Hooks,
69       Perlbal::Plugin::HighPriority.
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73perl v5.34.0                      2022-01-19  Perlbal::Manual::HighPriority(3)
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