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How do I change the read preference in MongoDB?
You must call Mongo. setReadPref() on the connection object before retrieving documents using that connection to use that read preference. To apply a read preference for a specific query or queries, you can apply cursor. readPref() to a cursor before iteration.
What is Readpreference in MongoDB?
Read preference describes how MongoDB clients route read operations to the members of a replica set. By default, an application directs its read operations to the primary member in a replica set (i.e. read preference mode “primary”). But, clients can specify a read preference to send read operations to secondaries.
How to query MongoDB secondary replica set members?
By calling rs.slaveOk () you are indicating to the system that you acknowledge that reads will be eventually consistent and wish to be able to query the secondary anyway.
When does a secondary become a primary in MongoDB?
A secondary can become a primary. If the current primary becomes unavailable, the replica set holds an election to choose which of the secondaries becomes the new primary. In the following three-member replica set, the primary becomes unavailable. This triggers an election where one of the remaining secondaries becomes the new primary.
When to use secondary preferred read preference in MongoDB?
Use the Secondary read preference when you must connect to a secondary. This would apply if you have a heavy read-only workload that should not be placed on the primary of the replica set. Use the Secondary Preferred read preference when access to a secondary is preferred, but not required.
What does write concern mean in MongoDB replica set?
Write Concern for Replica Sets. Write concern describes the level of acknowledgement requested from MongoDB for write operations. Read Preference. Read preference specifies where (i.e. which members of the replica set) the drivers should direct the read operations.