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candidate
manual.
Participation of a replica set node in the automated leader election can be turned on and off by this option.
The default value is ``off``. All nodes that have values other than ``off`` run the Raft state machine internally talking to other nodes according to the Raft leader election protocol. When the option is ``off``, the node accepts Raft messages from other nodes, but it doesn't participate in the election activities, and this doesn't affect the node's state. So, for example, if a node is not a leader but it has ``election_mode = 'off'``, it is writable anyway.
You can control which nodes can become a leader. If you want a node to participate in the election process but don't want that it becomes a leaders, set the ``election_mode`` option to ``voter``. In this case, the election works as usual, this particular node will vote for other nodes, but won't become a leader.
If the node should be able to become a leader, use ``election_mode = 'candidate'``.
Since version :doc:`2.8.2 </release/2.8.2>`, the manual election mode is introduced. It may be used when a user wants to control which instance is the leader explicitly instead of relying on the Raft election algorithm.
When an instance is configured with the ``election_mode='manual'``, it behaves as follows:
By default, the instance acts like a voter -- it is read-only and may vote for other instances that are candidates.
Once :ref:`box.ctl.promote() <box_ctl-promote>` is called, the instance becomes a candidate and starts a new election round. If the instance wins the elections, it becomes a leader, but won't participate in any new elections.
Default: 'off'
Environment variable: TT_ELECTION_MODE
Since version :doc:`2.6.1 </release/2.6.1>`. Specifies the timeout between election rounds in the :ref:`leader election process <repl_leader_elect>` if the previous round ended up with a split-vote.
In the :ref:`leader election process <repl_leader_elect_process>`, there can be an election timeout for the case of a split-vote. The timeout can be configured using this option; the default value is 5 seconds.
It is quite big, and for most of the cases it can be freely lowered to 300-400 ms. It can be a floating point value (300 ms would be ``box.cfg{election_timeout = 0.3}``).
To avoid the split vote repeat, the timeout is randomized on each node during every new election, from 100% to 110% of the original timeout value. For example, if the timeout is 300 ms and there are 3 nodes started the election simultaneously in the same term, they can set their election timeouts to 300, 310, and 320 respectively, or to 305, 302, and 324, and so on. In that way, the votes will never be split because the election on different nodes won't be restarted simultaneously.
Environment variable: TT_ELECTION_TIMEOUT
Since version :doc:`2.11.0 </release/2.11.0>`. In earlier Tarantool versions, use :ref:`election_fencing_enabled <cfg_election-election_fencing_enabled_deprecated>` instead.
Specifies the :ref:`leader fencing mode <repl_leader_elect_fencing>` that affects the leader election process. When the parameter is set to ``soft`` or ``strict``, the leader resigns its leadership if it has less than :ref:`replication_synchro_quorum <cfg_replication-replication_synchro_quorum>` of alive connections to the cluster nodes. The resigning leader receives the status of a :ref:`follower <repl_leader_elect>` in the current election term and becomes read-only.
In ``soft`` mode, a connection is considered dead if there are no responses for :ref:`4*replication_timeout <cfg_replication-replication_timeout>` seconds both on the current leader and the followers.
In ``strict`` mode, a connection is considered dead if there are no responses for :ref:`2*replication_timeout <cfg_replication-replication_timeout>` seconds on the current leader and :ref:`4*replication_timeout <cfg_replication-replication_timeout>` seconds on the followers. This improves chances that there is only one leader at any time.
Fencing applies to the instances that have the :ref:`election_mode <cfg_replication-election_mode>` set to ``candidate`` or ``manual``. To turn off :ref:`leader fencing <repl_leader_elect_fencing>`, set ``election_fencing_mode`` to ``off``.
Default: 'soft'
Environment variable: TT_ELECTION_FENCING_MODE
Networking
:ref:`io_collect_interval <cfg_networking-io_collect_interval>`
:ref:`net_msg_max <cfg_networking-net_msg_max>`
:ref:`readahead <cfg_networking-readahead>`
:ref:`iproto_threads <cfg_networking-iproto_threads>`
Since version 1.4.9. The instance will sleep for io_collect_interval seconds between iterations of the event loop. Can be used to reduce CPU load in deployments in which the number of client connections is large, but requests are not so frequent (for example, each connection issues just a handful of requests per second).
Environment variable: TT_IO_COLLECT_INTERVAL

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testing_project / Documentation: reference/configuration/index — English

To avoid the split vote repeat, the timeout is randomized on each node during every new election, from 100% to 110% of the original timeout value. For example, if the timeout is 300 ms and there are 3 nodes started the election simultaneously in the same term, they can set their election timeouts to 300, 310, and 320 respectively, or to 305, 302, and 324, and so on. In that way, the votes will never be split because the election on different nodes won't be restarted simultaneously.
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