问题
I come across the following phase and I had fair idea of distributed systems like hdfs and elasticsearch etc ..
A replica set in MongoDB is a group of mongod processes that maintain the same data set. Replica sets provide redundancy and high availability, and are the basis for all production deployments. This section introduces replication in MongoDB as well as the components and architecture of replica sets. The section also provides tutorials for common tasks related to replica sets.
In all those distributed systems like hdfs , elasticsearch - we can set the replication factor at the file level or index level. It seems it is not possible to do with mongo db, the only way to do the replication with mongodb is at the instance / process level - which means the machines in the replicaset group will have similar data no matter what.
Isnt it possible to create the replication at the db level ?
回答1:
In a MongoDB replica set, each document is stored on each node (hence the replication factor is the number of nodes, and it is not configurable).
The benefit of this design is each node can answer any query from its locally stored data, without needing to retrieve data from other nodes.
来源：https://stackoverflow.com/questions/64601659/mongodb-setting-the-replication-at-the-db-or-collection-level