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Update READ_ONLY_NODES.md

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Philip O'Toole
2022-07-15 09:30:25 -06:00
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DOC/READ_ONLY_NODES.md
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# Read-only nodes
rqlite supports adding _read-only_ nodes. You can use this feature to add read scalability to the cluster if you need a high volume of reads, or want to distribute copies of the data nearer to clients -- but don't want those nodes counted towards the quorum. These types of nodes are also known as _non-voting_ nodes.
What this means is that a read-only node doesn't participate in the Raft consensus system i.e. it doesn't contribute towards quorum, nor does it cast a vote during the leader election process. Just like voting nodes, however, read-only nodes still subscribe to the stream of committed log entries broadcast by the leader. Read-only nodes update the local SQLite database, and in every other sense act like any other node in the cluster.
What this means is that a read-only node doesn't participate in the Raft consensus system i.e. it doesn't contribute towards quorum, nor does it cast a vote during the leader election process. Just like voting nodes, however, read-only nodes still subscribe to the stream of committed log entries broadcast by the Leader, and update the SQLite database using the log entries they receive from the Leader.
## Querying a read-only node
Any read request to a read-only node must specify [read-consistency](https://github.com/rqlite/rqlite/blob/master/DOC/CONSISTENCY.md) level `none`. If any other consistency level is specified (or no level is explicitly specified) the read-only node will redirect the request to the leader.