The MongoDB\Driver\ReadConcern class

简介

MongoDB\Driver\ReadConcern controls the level of isolation for read operations for replica sets and replica set shards. This option requires the WiredTiger storage engine and MongoDB 3.2 or later.

类摘要

预定义常量

MongoDB\Driver\ReadConcern::LINEARIZABLE

A linearizable read avoids returning reads from a stale primary (one that has already been superseded by a new primary but doesn't know it yet).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 this read concern level does not by itself produce linearizable reads; they must be issued in conjunction with MongoDB\Driver\WriteConcern::MAJORITY writes to the same document(s) in order to be linearizable.

MongoDB\Driver\ReadConcern::LOCAL

Queries using this read concern will return the node's most recent copy of the data. This provides no guarantee that the data has been written to a majority of the nodes (i.e. it may be rolled back).

This is the default read concern level.

MongoDB\Driver\ReadConcern::MAJORITY

Queries using this read concern will return the node's most recent copy of the data confirmed as having been written to a majority of the nodes (i.e. the data cannot be rolled back).

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