DynamoDb Notes

DynamoDb is a NoSQL database, which to me means it’s schema-less, scales horizontally, and has incredible performance when accessing data via K/V pairs.  I’m adding this here as writing about it helps me remember.

  • Two types of primary key
    • Partition key
      • same as a primary key
      • must be unique scalar attribute
      • internally also known as a hash attribute, because of the internal hash function (e.g. EmployeeId)
      • tells what “partition” the item will be stored at
    • Parition key and Sort key
      • same as a composite primary key
      • the partition key is not unique, but becomes unique when combined with the sort key (e.g. Artist & Song)
      • sort key is internally also known as a range attribute
      • partition tells where it is and sort key sorts the item
  • Secondary index
    • use when you want to query using an alternate key in addition to the partition key
    • creating an index “projects” your chosen attributes, from the base table, into a data structure
    • Two types of secondary index
      • Global secondary index
        • an index of either (1) a partition key only or (2) a composite (partition & sort), that can be different than the table’s
        • spans all partitions
        • can only have 5 indexes
        • no size restriction of all indexed
        • eventual consistency
        • can be added/deleted even after table creation
      • Local secondary index
        • same partition key as the table’s, but with a different sort key
        • spans only one table based on the partition key of the table
        • can only have 5 indexes
        • 10 GB or less in size for all indexed
        • eventual or strong consistency
        • cannot be added/deleted after table creation
  • DynamoDb Streams
    • perfect for DB cross-replication
    • must be turned on for a table
    • each event is a stream record
    • TTL of 24 hours
    • can be used with AWS Lamdba to create trigger (e.g. send “Welcome” email when new stream record is received, via a new item write)

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