# AWS Databases Notes

Hello Readers,

This is part 3 of the 5-part Series on cracking the AWS Solutions Architect - Associate Exam.  [Click here](https://blog.hellokarthic.com/aws-ec2-notes)  for part 2 - AWS EC2.

I've divided the notes into a 5 part series.

- **Part 1:**  [Introduction and AWS S3](https://blog.hellokarthic.com/aws-saa-notes) 
- **Part 2:**  [AWS EC2](https://blog.hellokarthic.com/aws-ec2-notes) 
- **Part 3:**  [Databases](https://blog.hellokarthic.com/aws-db-notes) 
- **Part 4:**  [DNS, VPC, and HA(High-Availability)](https://blog.hellokarthic.com/aws-dns-vpc-ha-notes) 
- **Part 5:**  [Application Services and Serverless + Bonus](https://blog.hellokarthic.com/aws-applications-serverless-notes) 

### Database Notes
---
#### Database in AWS:

 1. **RDS** (OLTP-Online transaction processing) - Ex: give order ID, returns all data
	- SQL Server
	- Oracle
	- MySQL Server
	- PostgreSQL
	- Aurora
	- MariaDB
 2. **NoSQL**
	- DynamoDB
 3. **Data Warehouse** (OLAP-Online analytical processing) - For complex analytics & BI.
	- Redshift
 4. **Elasticache** - improves the performance of DB by caching frequent queries.

	- Two types
		- Memcache
		- Redis
	- You can set up an Autoscaling group that can auto-scale Cache nodes based on CPU usage.

#### Key Features of RDS
- Multi-AZ - For disaster recovery
- Read Replicas - For Performance ( Max 5 copies for a DB )

#### Types of RDS backups
- Automated Backups 
	- point-in-time recovery; 
	- Retention period - 1 to 35 days;
	- Backups stored in S3 (for free)
	- Takes 1 daily snapshot and transactional logs.
	- These are deleted when RDS is deleted
- Database Snapshots
	- Manual snapshots
	- These are NOT deleted when RDS is deleted

#### General RDS Notes
- [NEW] You can autoscale using RDS Auto Scaling groups
- Two ways to cope with heavy DB load - Elasticache & Read replica
- **Read replica** is mainly for Performance
- **Multi-AZ** is mainly for Disaster Recovery
- Cross-region Read replica can be created for Disaster Recovery

#### DynamoDB
- Stored on SSD - Hence fast
- Spread across 3 AZ
- DynamoDB allows for the storage of large text and binary objects, but there is a limit of **400 KB**.
- Has DAX(DynamoDb Accelerator) - in-memory cache(for performance) - It is similar to Elasticache for RDS.
- Two types:
	- Eventual consistency Read (default) - takes around 1 second to update
	- Strong consistency Read - updates Within 1 second and can be read

#### RedShift
- Single Node ( 160Gb )
- Multi-Node
	- **Leader Node** (manages client connection and received requests)
	- **Compute Node** (Stores data and performs computations). Up to 128 nodes.
- Has Advanced Compression -Columnar compression(data in the column is of the same type)
- Massively Parallel Processing (MPP)
- Backups are taken by default with 1-day retention. & Max = 35 days (similar to RDS)
- It maintains 3 copies of data - Original & Replica on the compute node. Backup in S3.
- Charged only for compute node - Not for Leader node
- **No multi-AZ support. It can only be in 1 AZ.**

#### Aurora
- Start with 10GB. Scales in 10Gb Increments. Up to 64TB
- Compute resource up to 32vCPUs and 244Gb of memory
- **2 copies in each AZ. Minimum of 3 AZ. So 6 copies of your data.**
- Types of Aurora replicas:
	- Aurora Replicas (max 15)
	- MySQL Read Replicas (max 5)
	- PostgreSQL (max 1)

![image.png](https://cdn.hashnode.com/res/hashnode/image/upload/v1609074911848/xOiR3H4On.png)

#### Aurora Serverless
- Simple Cost-effective option for infrequent, intermittent, or unpredictable workloads
- Automatically start-up shut down, and scale capacity up or down based on your 
application's needs

Continue reading  [Part 4 - AWS Route53, VPC, and HA](https://blog.hellokarthic.com/aws-dns-vpc-ha-notes) ...