AWS Dynamo DB

The topics you need to know for the Dynamo DB:

• Primary Key
• RCU / WCU
• APIS
• Query VS Scan
• GSI
• LSI
• Stream
• TTL
• Transection
• Dynamo DB as session state cache
• Write Types
• Fast, Flexible No SQL Database
• Single digit ms latency, fully managed
• Supports document and key-value(web, gaming, ad-tech, IOT)
• Table, Item(row), attribute ( key-value )
• Writes are written into 3 different location/facilities/datacenter (synchronous) 
• Synchronously replicates data across the three facilities in AWS region, Giving you high availability and data durability.
• Optimistic locking
• Conditional Updates
• TTL Expiry Date ( Epoch format)
• Amazon DMS : migrate to dynamoDB from mongo oracl, mysql etcs
• Primary Key 
• Two types of primary key
  • Single Attribute( Unique Id) : Partition key (Hash Key) composted of 1 attribute 
    •  No Nesting allowed here
    •  It helps to determine the physical location of data
  • Composite Key( Unique id and Range) : Partition Key (Hash Key) and Sort Key ( Range Key) eg, date
    • Composed of two attributes
    • If two data has same partition key then it must have a different sort key 

• Secondary Indexes 
• Local Secondary Index
  • Same Partition Key + Different Sort Key 
    • Can only be created while creating the table, Can’t be added/removed or modified later
  • Global Secondary Index
    • Different Partition Key + Different Sort Key
    • Can be created during the table creation and Can be added 
    • later or remove/modify later
• Query VS Scan
  • ProjectionExpression  parameter : Only returns a selected attributes.
  • Query Operation is more efficient then Scan Operation
  • For Quick response time design Use
  • Query Get or BatchGetItem ( read multiples items, Can get upto 100 items or upto 16MB of Data

Query	Scan
Find items in a table by using only primary key attributes. Must provide partition attribute name and the value to searchOptionally provide a sort key attribute name and value to refine search	Examine every item
By default, Returns all the data attributes for those items with specified primary keys	By default, Returns all the data attributes
Results are always sorted by the sort key (By default,ascending for both number and string). To reverse the sort order set the ScanIndexForward Parameter to false
By default, Going to be eventually consistent
	Max limit of data can be retrieved by a scan operation: 1MB

• RCU / WCU
• Provisioned Throughput
  • Read Provisioned Throughput
    • RCU Price per hour : $0.00013
    • All units are rounded upto 4KB
    • Strongly reads 4KB items 1 read :  4KB chunks * no of items 
    • Eventually reads 4KB items 2 reads :  4KB chunks * no of items / 2
  • Write Provisioned Throughput 
    • WCU Price per hour : $0.00065
    • All units are rounded up to 1 KB
    • Strongly  consist of 1KB item 1 write per second : 1KB * no of items
    • Eventually  consist of 2KB item 1 write per second : 2KB * no of items
• ProvisionedThroughputExceedExpection : 
  • 400 HTTP Status code
  • Exceed maximum allowed provisioned throughput for a table
  • Exceed maximum allowed One or more global secondary index
  • Exceed particular hash key
• ProvisionedThroughput 
  • Per account for US East 80K read and 80K write
              For other region 20K
• Smallest amount of reserved capacity 100RCU or 100WCU
• AssumeRoleWithWebIdentity : role
• Idempotent Conditional write
  • Must use If data is critical and no margin of error 
• Atomic counter : always need to increment so its not Idempotent
• DAX(Dynamo DB Accelerator)
  • Dedicated service designed to cache DynamoDB request
    • Automatically add the data in DAX if there is cache miss or update the data if it is updated in the table
• Total Number of tables per region :
  •  256 tables per region
• Maximum limit of data that can be retrive from scan operation is : 
  • 1MB
• BatchGetItem returns Maximum of : 
  • 16MB or 100 items 
• Maximum Allowed Scondary index per Dynamo DB : 
  • 25( 20 Global + 5 Local )
• Maximum Collection Size of Items in Dynamo DB : 
  • 10 GB
• Maximum size of items in Dynamo Table :
  •  400 KB ( 5 TB in S3 bucket)
• ItemCollectionSizeLimitExceedException :
  • Size of group of items with the same partition key value has exceeded 10GB.
• Strategy : Optimistic concurrency control/lock