From 705153df0c1697bf52c97895d865e4c531b86daf Mon Sep 17 00:00:00 2001 From: Bob Grabar Date: Fri, 28 Jun 2013 11:57:23 -0400 Subject: [PATCH] readability: rs-high-availability Old --- file: build/rs-high-avail/json/core/replica-set-high-availability.json source: source/core/replica-set-high-availability.txt stats: coleman-liau: 13.962537313432836 flesch-ease: 19.15201492537315 flesch-level: 15.343624733475483 foggy: count: 39 factor: 0.1455223880597015 threshold: 3 sentence-count: 14 sentence-len-avg: 19 smog-index: 12.66393586644259 word-count: 268 New --- file: build/rs-high-avail/json/core/replica-set-high-availability.json source: source/core/replica-set-high-availability.txt stats: coleman-liau: 12.920875912408757 flesch-ease: 29.79033230887441 flesch-level: 12.686765270841338 foggy: count: 35 factor: 0.12773722627737227 threshold: 3 sentence-count: 19 sentence-len-avg: 14 smog-index: 10.882677951670543 word-count: 274 --- source/core/replica-set-high-availability.txt | 52 ++++++++++--------- 1 file changed, 27 insertions(+), 25 deletions(-) diff --git a/source/core/replica-set-high-availability.txt b/source/core/replica-set-high-availability.txt index bf08d755802..05fd2b5bcea 100644 --- a/source/core/replica-set-high-availability.txt +++ b/source/core/replica-set-high-availability.txt @@ -9,36 +9,38 @@ Replica Set High Availability .. default-domain:: mongodb -Replica sets provide automatic failover to support autonomous -operation. If the :ref:`primary ` of a -replica set either steps down, becomes inaccessible, or becomes -otherwise ineligible to act as the primary, the replica set will -automatically hold an :doc:`election ` to -:doc:`elect ` one of the secondaries to -become primary. In some situations, the failover process may also -involve :doc:`rollbacks `. - -In most cases, failover occurs without administrator intervention. -However, if your MongoDB deployment does not failover accordingly, -consider both ability of the remaining members to form a majority as -well as the member eligibility to become primary. For instance, -network partitions can render some members inaccessible, and the -remaining members are unable to form a majority. Design your deployment -to ensure that a majority of set members can elect a primary in the -same facility as the core application systems. Additionally, to be -eligible to become primary, members must have a +:term:`Replica sets ` provide high availability through +automatic :term:`failover`. Automatic failover allows a +:term:`secondary` member of the replica set to become the +new :term:`primary` should the primary become inaccessible. + +Within a replica set, members hold the same information but are +otherwise autonomous. If the primary becomes inaccessible for any +reason, the replica set automatically holds an :doc:`election +` for a new primary. In some situations, +the failover process may also involve :doc:`rollbacks +`. + +You must configure your replica set correctly for failover to work. +Locate a majority of the replica set's voting members in one data +center. The center should hold all the members that are eligible to +become primary. Choose the facility that contains your core application +systems. Without these design patterns, network partitions might render +some members inaccessible, and the remaining members will not be able to +form a majority. + +To be eligible to become primary, a member must have a :data:`~local.system.replset.settings.members[n].priority` setting -greater than ``0``, have a state that is less than ten seconds behind -the last operation to the :term:`replica set`, and generally be *more* -up-to-date than the voting members. +greater than ``0`` and have a state that is fewer than ten seconds +behind the last operation to the replica set. Also, the member usually +must be *more* up-to-date than the voting members. Failover Processes ------------------ -To recover from the loss or inaccessiblity of the current primary, the -replica set failover processes involve an :doc:`election -` to elect a new primary, and, in certain -situations, :doc:`rollbacks `. +To recover from the loss or inaccessibility of the current primary, the +replica set holds an election. In rare situations, the replica set also +"rolls back" write operations. .. include:: /includes/dfn-list-replica-set-high-availability.rst