AWS notes

Dynamo DB ( No SQL DB )

Amazon DynamoDB

- No Query joins
- No Aggregations such as 'SUM','AVG'
- Horizontal Scaling
- Millions of requests per seconds, trillions of row, 100s of TB of storage
- Enables event driven programming with DynamoDB Streams
- Low cost and auto-scaling capabilities
- Standard & Infrequent Access (IA) Table Class

DynamoDB - Basics

- DynamoDB is made of Tables
- Each table can have an infinite number of items
- Each item has attributes (can be added over time – can be null)
- Maximum size of an item is 400KB
- Data types supported are:
	-Scalar Types – String, Number, Binary, Boolean, Null
	-Document Types – List, Map
	-Set Types – String Set, Number Set, Binary Set




DynamoDB - Read/Write Capcity Modes

- Control how you manage your table’s capacity (read/write throughput)
-Provisioned Mode (default)
	You specify the number of reads/writes per second
	You need to plan capacity beforehand
	Pay for provisioned read & write capacity units
-On-Demand Mode
	Read/writes automatically scale up/down with your workloads
	No capacity planning needed
	Pay for what you use, more expensive ($$$)
-You can switch between different modes once every 24 hours

R/W Capacity Modes – Provisioned
	
	Table must have provisioned read and write capacity units
	Read Capacity Units (RCU) – throughput for reads
	Write Capacity Units (WCU) – throughput for writes
	Option to setup auto-scaling of throughput to meet demand
	Throughput can be exceeded temporarily using “Burst Capacity”
	If Burst Capacity has been consumed, you’ll get a “ProvisionedThroughputExceededException”
	It’s then advised to do an exponential backoff retry

WCU is ignored as we won't be doing many writes on the Dynamo DB

Dynamo DB has 2 kinds of read-modes

Strongly Consistent Read vs. Eventually Consistent Read
	Eventually Consistent Read (default)
		If we read just after a write, it’s possible we’ll get some stale data because of replication
	Strongly Consistent Read
		If we read just after a write, we will get the correct data
		Set “ConsistentRead” parameter to True in API calls (GetItem, BatchGetItem, Query, Scan)
		Consumes twice the RCU ( $$$ & more latency )


RCU 

	One Read Capacity Unit (RCU) represents one Strongly Consistent Read per second, or two Eventually Consistent Reads per second, for an item up to 4 KB in size
	If the items are larger than 4 KB, more RCUs are consumed and going to be rounded up to the nearest upper KB
	
	
Item Size : https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/WorkingWithItems.html