DynamoDB - Basic APIs¶

Writing data¶

• PutItem
  • Creates a new item of fully replace an old item (same primary key)
  • Consumes WCU
• UpdateItem
  • Edits an existing item's attributes or adds a new item if it doesnt exist
  • Can be used to implement Atomic Counters - a numeric attribute that's unconditionally incremented
• Conditional Writes
  • Accept a write/update/delete only of conditions are met, otherwise returns an error
  • Helps with concurrent access to items
  • No performance impact

Reading data¶

• GetItem
  • Read based on Primary Key
  • Primary Key can be HASH or HASH+Range
  • Eventually Consistent Read (default)
  • Option to use Strongly Consistent Reads (more RCU - might take longer)
  • ProjectionExpression can be specified to retrieve only certain attributes
• Query
  • returns items based on:
    • KeyConditionExpression
      • Partition Key value (must be = operator) - required
      • Sort key value (=, <, <=, >, >=, between, begins with) - optional
    • FilterExpression
      • Additional filtering after the query operation (before data is returned to you)
      • Use only with non-key attributes (does not allow HAS or RANGE attributes)
  • returns
    • The number of items specified in Limit
    • Or up to 1 MB of data
  • Ability to do pagination on the results
  • Can query table, a Local Secondary Index, or a Global Secondary Index
• Scan
  • scan the entire table and then filter out data (inefficient)
  • Returns up to 1MB of data - use pagination to keep on reading
  • Consumes a lot of RCU
  • Limit impact using Limit or reduce the size of the result and pause
  • For faster performance, use Parallel Scan
    • Multiple workers scan multiple data segments at the same time
    • Increases the thoughput and RCU consumed
    • Limit the impact of parallel scans just like you would for scans
  • Can use ProjectionExpression & FilterExpression (no changes to RCU)

Deleting data¶

• DeleteItem
  • Delete an individual item
  • Ability to perform a conditional delete
• DeleteTable
  • Delete a whole table and all it's items
  • Much quicker deletion than calling DeleteItem on all items

Batch Operations¶

• Allows you to save in latency by reducing the number of API calls
• Operations are done in parallel for better efficiency

• Part of a batch can fail, in which case we need to try again for the failed items

• BatchWriteItem

  • Up to 25 PutItem and/or DeleteItem in one call
  • Up to 16MB of data written, up to 400KB of data per item
  • Can't update items (use UpdateItem)
• BatchGetItem
  • Return items from one or more tables
  • Up to 100 items, up to 16MB of data
  • Items are retrieved in parallel to minimize latency