DynamoDB   AWS

AWS DynamoDB

 · 3 mins read

DynamoDB

Fully managed NoSQL database that provides low-latency access at scale

Usage patterns

  • Apps needing low-latency NoSQL database able to scale storage and throughput up or down without code changes or downtime
  • Mobile apps and gaming
  • Sensor networks
  • Digital and serving
  • E-commerce shopping carts

Cost

  • Three components:
    • Provisioned throughput capacity (per hour)
    • Indexed data storage (per GB per month)
    • Data transfer in or out (per GB per month)

Performance

  • SSDs and limiting indexing on attributes provides high throughput and low latency

  • Define provisioned throughput capacity required for your tables

  • Fault tolerance: automatically synchronously replicates data across 3 data centers in a region

Durability and avaiability

  • Protection against individual machine or facility failures
  • DynamoDB Streams allows replication across regions
  • DynamoDB Streams enables tables data activity replicated across geographic regions

Scalability and elasticity

  • No limit to data storage, automatic storage allocation, automatic ddata partition

Interfaces

  • REST API allows management and data interface
  • DynamoDB select operation creates SQL-like queries

Anti-patterns

  • Port application from relational database
  • Joins or complex transactions
  • Large data with low I/O rate
  • Blob (Binary Large Object) data > 400KB, S3 better choice

Operational Characteristics of DynamoDB in detail

  • DynamoDB tables
    • Attributes are the columns
    • Items are the rows
    • Tables are a collection of items
    • Must have a primary key, two types:
      • Partition key: primary key with one attribute called the hash attribute
        • DynamoDB has function determines the partition where an item is located
      • Composite primary key: partition key plus sort key (range attribute) where all items with the same sort key are located together ordered by sort key value
    • No limit to number of items (rows) in a table
    • Maximum item size is 400KB
  • DynamoDB has two models of consistency: eventual and strong consistency
    • Eventually consistent reads are the default
      • Achieves maximum read throughput (Performance +)
      • May return stale data (Accuracy -)
    • Strongly consistent reads
      • Returns result representing all prior write operations
      • Always accurate data returned (no stale data) (Accuracy +)
      • Increased latency with this option (Performance -)
  • Atomicity, consistency, islolation, and durability (ACID)
    • Support for ACID transactions using transactional read and write APIs
    • ACI across one or more tables in one account and region
    • Use for transactions that require coordinated inserts, updates, or deletes to multiple items as part of one logical operation
  • Cost versus performance - two capacity modes
    • On-demand capacity
      • DynamoDB automatically provisions capacity based on your workload, up or down
    • Provisioned capacity
      • Specify read capacity units (RCUs) and write capacity units (WCUs) per second for your application
      • One RCU equals one strongly consistent read or two eventually consistent reads per second for items to up to 4 KB
      • One WC equals one write per second for items to up to 1 KB
      • Can use auto scaling to automatically calibrate our table’s capacity
        • Helps manage cost
  • DynamoDB Global tables
    • Specifiy multple in which our table is available
    • DynamoDB propagates all changes across all regions
    • Any change to an item in any replica is propagated to all other replicas
    • New items propagated within seconds
    • Uses last-writer-wins reconciliation with concurrent updates
    • When a table in a region has issues, application directs to a different region

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