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A. DynamoDB - Simple Operations 📚

1. Read

1.1. 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
  • to retrieve only certain attributes

1.2. Scan

  • Scan the entire table and then filter out data
  • ProjectionExpression
  • FilterExpression
  • Consumes a lot of RCU
  • For faster performance, use Parallel Scan
  • can use limit and pagination.

2. Write

2.1 PutItem

  • Creates a new item
  • or fully replace an old item (same Primary Key)
  • Consumes WCUs

2.2 UpdateItem

  • Edits an existing item’s attributes
  • or adds a new item if it doesn’t exist
  • use Atomic Counters

3. Query

  • returns Item/s based on below expression:
  • KeyCondition :
    • on partitionKey
    • on sortKey
  • Filter
    • addition filter on other attributes.
  • set limit
  • no of item
  • size. eg : 1 MB data.
  • perform pagination
  • index ?
  • local secondary ?
  • Global Secondary ?

4. Delete

4.1 DeleteItem

  • delete an individual item
  • Ability to perform a conditional delete

4.2 DeleteTable

  • Delete a whole table and all its items
  • Much quicker deletion than calling DeleteItem on all items
  • table cleanup
  • option-1: DeleteTable and recreate it. fast, cheap
  • option-2: scan and delete individual item. slow, consumes RCU/WCU

B. DynamoDB - Batch Operations 📚

  • reducing the number of API calls
  • done in parallel for better efficiency

1. BatchWriteItem

  • Up to 25 PutItem and/or DeleteItem in one call
  • Up to 16 MB of data written, up to 400 KB of data per item
  • Can’t update items (use UpdateItem)
  • error: UnprocessedItems for failed write operations
  • exponential backoff
  • add WCU

2. BatchGetItem

  • Return items from one or more tables
  • Up to 100 items, up to 16 MB of data
  • Items are retrieved in parallel to minimize latency
  • error: UnprocessedKeys for failed read operations
  • exponential backoff
  • add RCU

C. Types of write (4)

img_1.png

1. concurrent write

2. Atomic write

3. batch Write

4. conditional Write (optimistic locking)

  • Accept a write/update/delete only
  • if conditions are met,
  • otherwise returns an error
  • Helps with concurrent access to items
  • No performance impact
  • use these function in conditional expression
  • attribute_exists()
  • attribute_not_exists()
  • attribute_type()
  • contains() (for string)
  • begins_with() (for string)
  • ProductCategory IN (:cat1, :cat2) and Price between :low and :high
  • size() (string length)

program

1. py : conditional write ( optimistic locking)

  • https://us-west-2.console.aws.amazon.com/lambda/home?region=us-west-2#/functions/dynamodb-ps-games-operation?tab=code
  • https://us-west-2.console.aws.amazon.com/dynamodbv2/home?region=us-west-2#item-explorer?operation=SCAN&table=ps-games

{
  "id": { "N": "101" },
  "name": { "S": "The Last of Us Part II" },
  "release_year": { "N": "2020" },
  "genre": { "S": "Action-Adventure" },
  "developer": { "S": "Naughty Dog" },
  "rating": { "N": "9.5" },
  "platforms": { "SS": ["PS4", "PS5"] },
  "multiplayer": { "BOOL": false },
  "file_size": { "N": "80" },
  "version" : { "N", "1"}
}

import boto3
from decimal import Decimal

dynamodb = boto3.resource('dynamodb')
table = dynamodb.Table('playstation-games')

# Use Decimal for numeric values
try:
    table.update_item(
        Key={"id": 101, "name": "The Last of Us Part II"},
        UpdateExpression="SET rating = :new_rating, version = version + :incr",
        ConditionExpression="version = :expected_version",
        ExpressionAttributeValues={
            ":new_rating": Decimal('9.6'),  # Use Decimal instead of float
            ":expected_version": Decimal('1'),
            ":incr": Decimal('1')
        }
    )
    print("Update successful!")
except dynamodb.meta.client.exceptions.ConditionalCheckFailedException:
    print("Version mismatch! Item was updated by another process.")

aws dynamodb update-item \
  --table-name ps-games \
  --key '{
      "id": {"N": "101"},
      "name": {"S": "The Last of Us Part II"}
  }' \
  --update-expression "SET rating = :new_rating, version = version + :incr" \
  --condition-expression "version = :expected_version" \
  --expression-attribute-values '{
      ":new_rating": {"N": "9.6"},
      ":expected_version": {"N": "1"},
      ":incr": {"N": "1"}
  }' \
  --region us-west-2