• "local"

Read Concern "local"

A query with read concern "local" returns data from the instancewith no guarantee that the data has been written to a majority of thereplica set members (i.e. may be rolled back).

Read concern "local" is the default for:

• read operations against primary
• read operations against secondaries if the reads are associated withcausally consistent sessions.

Regardless of the read concern level, the most recent data on anode may not reflect the most recent version of the data in the system.

Causally Consistent Sessions

Read concern local is available for use with causallyconsistent sessions.

Read Concern "local" and Transactions

You set the read concern at the transaction level, not at theindividual operation level. To set the read concern for transactions,see Transactions and Read Concern.

Example

Consider the following timeline of a write operation Write₀ toa three member replica set:

Note

For simplification, the example assumes:

• All writes prior to Write0 have been successfullyreplicated to all members.
• Writeprev is the previous write before Write0.
• No other writes have occured after Write0.

Then, the following tables summarizes the state of the data that a readoperation with "local" read concern would see attime T.