Hedged Read Option
Starting in MongoDB 4.4 for sharded clusters, you can specify the use
of hedged reads for non-primary
read preferences.
With hedged reads, the mongos instances can route read
operations to two replica set members per each queried shard and return
results from the first respondent per shard.
Hedged reads are supported for the following operations:
To specify hedged read for a read preference, MongoDB 4.4 introduces the hedged read option for read preferences.
Enable Hedged Reads
To use hedged reads, enable the hedge read option for non-primary
read preferences. Read preference nearest specifies hedged
read by default.
When using the drivers, refer to the drivers' read preference API.
When using
mongosh, you can use the helper methodscursor.readPref()andMongo.setReadPref().
Additional Information
For more information on hedged reads, see Hedged Reads.
Member Selection with Hedged Reads
For details on member selection for hedged reads, see Read Preference and Shards.
Hedged Reads Diagnostics
The command serverStatus and its corresponding
mongosh method db.serverStatus() return
hedgingMetrics.