One search. Connected ideas.

A transaction makes several database operations commit or roll back as a unit. MongoDB already makes single-document writes atomic, so a transaction is mainly needed when one business rule spans multiple documents. A session supplies transaction context; every participating operation must use that context.

Read concern, write concern and read preference control different parts of consistency and availability. Read concern controls which data a read may observe, write concern controls required acknowledgement, and read preference chooses eligible replica members. Combining them deliberately matters when an application expects to read a recent write or survive failover.

Replication keeps copies of data so a system can recover from node failure, while sharding distributes different subsets of data across nodes. Replica sets improve redundancy; sharding spreads storage and workload. A sharded deployment can also replicate each shard, so these techniques are complementary.

A transaction makes several database operations commit or roll back as a unit. MongoDB already makes single-document writes atomic, so a transaction is mainly needed when one business rule spans multiple documents. A session supplies transaction context; every participating operation must use that context.

Read concern, write concern and read preference control different parts of consistency and availability. Read concern controls which data a read may observe, write concern controls required acknowledgement, and read preference chooses eligible replica members. Combining them deliberately matters when an application expects to read a recent write or survive failover.

Replication keeps copies of data so a system can recover from node failure, while sharding distributes different subsets of data across nodes. Replica sets improve redundancy; sharding spreads storage and workload. A sharded deployment can also replicate each shard, so these techniques are complementary.

MongoDB & Mongoose learning module