What are the more important MongoDB features?

• Indexes

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  • Improves performance for frequent queries
  • Indexes are based on a field or set of fields
  • Queries containing only indexed fields are optimal
  • Can affect other operations such as sort()
  • Main Types: single field and compound
  • Other types: multikey, geospatial, text, hashed
  • Properties: unique, sparse

• Distributed queries

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  • Sharded clusters allow you to partition a data set
  • Reads are most efficient when directed to a specific shard
  • Scatter gather queries (no shard key) can be inefficient

• Read preferences

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  • Allows you to control queries (reads)
  • Concerns replica sets
  • Modes: primary, primaryPreferred, secondary,
    secondaryPreferred, nearest

• Distributed write operations

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  • Directs write operations from apps to shard clusters
  • Partitions data into ranges based on value of the shard key
  • Write operations go to the primary
  • Secondaries continuously replicating the primary oplog
    and apply the operations to themselves
  • Write concerns can apply

• Write concerns

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  • Guaranteed delivery
  • Stronger settings: slower, better guarantee
  • Levels: Errors Ignored, Unacknowledged, Acknowledged,
    Journaled, Replica Acknowledged

• Query plans and optimizers

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  • Optimizer processes queries
  • Chooses the most efficient query plan
  • Over time deletes and re-evaluates the plan