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DynamoDB

Concepts

  • NoSQL - DBaaS - Key/Value & Document
  • No self managed servers or infrastructure
  • Manual/Automatic provisioned performance IN/OUT or On-Demand
  • Highly Resiliient .. accross AZs and optionally global
  • Really fast .. single-digit milliseconds (SSD based)
  • Backups, point-time-recovery, encryption at rest
  • Event-Driven Integration

Tables

  • A table is grouping of ITEMS with the same primary key
  • PRIMARY KEY
  • Simple partition key (PK) => Simple
  • Partition Key (PK) and Sort Key (SK) => Composite
  • DDB has no rigid attribute schema
  • Each iterm MUST have a unique value for PK and SK
    • Item max size - 400KB

Capacity - Speed

WCU = Write Capacity Unit RCU = Read Capacity Unit - 1 WCU = 1KB per second - 1 RCU = 4KB per second


dynamo-tables

On-Demand Backups

  • Full copy of table - retained until removed
  • Restore
    • Same or Cross region
    • With or Without Indexes
    • adjust Encryption Settings

Point-in-time Recovery (PITR)

  • Enabled on the table - disabled by default
  • 35 day recovery window
    • Continuous record of changes allows replay to any point in the window
  • 1 second grnularity

Operations

Provisioned On-Demand
for unkonw, unpredicatable, low admin RCU and WCU set at tables
cost per million R or W unts every operation consumes at least 1 RCU/WCU*
> Every table has a RCU and WCU burst pool (300 seconds)
> Provisioned Throughput Exception
  • Query - using PK and SK (optional)
    • Capacity consumed is the size of all returned items
  • Scan - moves through a table consuming the capacity of every ITEM

Consistency Model

Eventual Cosistent Strongly Consistent
Writes are replicated to non-leader nodes eventually (ms) Writes are replicated to non-leader nodes eventually (ms)
No guaranted updated data - reads from non-leader nodes Always read from the leader node gurantees updated data
Cheaper than eventual Pricier than eventual

Indexes

  • GSI - Global Secondary Indexes
    • can be created at any time
    • 20 per base table by default
    • alternative PK and SK
    • GSIs have their own RCU and WCU allocations
    • Attributes - ALL, KEYS_ONLY, INCLUDE
    • ALWAYS EVENTUALLY CONSISTENT
  • LSI - Local Secondary Indexes
    • alternative view for a table
    • must be created with table (when strong consistency is required)
    • 5 LSI's per base table
    • alternative SK on the table
    • shares the RCU and WCU with the table
    • Attributes - ALL, KEYS_ONLY, INCLUDE

Streams

  • Time ordered list of ITEM Changes in a table
  • 24-Hour rolling window
  • Enabled on a per table basis
  • Records INSERTS, UPDATES and DELETES
  • Different view types influence what is in the stream
  • View Types
    • KEYS_ONLY
    • NEW_IMAGE
    • OLD_IMAGE
    • NEW_AND_OLD_IMAGES

Triggers

  • Item changes generate an event
  • That event contains the data which changed - what depending on the view type
  • A action is taken on that data
  • AWS => Streams + Lambda
  • Reporting & Analytics
  • Aggregation, Messaging or Notifications

DynamoDB Accelerator - DAX

  • In-memory cache designed specifically for DynamoDB
  • Applications calls DAX using DAX SDK which eliminates the overhead of application checking cache for every call.
  • DAX is deployed within the VPC
  • Primary NODE (Writes) and Replicas (Read)
  • Nodes are HA .. Primary failure = election
  • In-Memory cache - Scaling - faster reads, reduced costs
  • Both vertical and horizontal scaling
  • Supports write-through
    • writes the data as well as cache it

Global Tables

  • Global table provides multi-master cross-region replication
  • Tables are created in mutiple regions and added to the same global table (becoming replica tables)
  • Last writer wins is used for conflict resolution
  • Reads and Writes replication between regions

  • Strongly consistent reads ONLY in the same region as writes

    • Global eventual consistency for different regions tables

  • Multi-master replication

    • Data is replicated within a second
    • All tables can be used for Read and Write operations

  • Provides Global HA and Global DR/BC

Time-To-Live - TTL

Amazon DynamoDB Time to Live (TTL) allows you to define a per-item timestamp to determine when an item is no longer needed.

While deleting the item once the item TTL is expired, no capacity units is consumed for the actions.

dynamo-ttl