|0||Reads available data.|
|1||Reads data committed locally.|
|2||Reads data committed to a majority of nodes.|
|3||Avoids returning data from a "stale" primary (one that has already been superseded by a new primary but doesn't know it yet). It is important to note that readConcern level linearizable does not by itself produce linearizable reads; they must be issued in conjunction with w:majority writes to the same document(s) in order to be linearizable.|
|4||Snapshot read concern level.|
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