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11. Database and Analytics
Database Kinds
Operational DBs
Analytical DBs
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Operational DBs

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Amazon ElastiCache

Memcached vs Redis
Caching Strategies
Amazon ElastiCache is a fully managed in-memory data store and cache service that supports two popular open-source caching engines, Redis and Memcached. It is designed to improve the performance of web applications by enabling you to retrieve information from fast, managed, in-memory caches instead of relying entirely on slower disk-based databases. It’s a key/value store.
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Key Features:

In-Memory Caching:
Significantly improves latency and throughput for read-heavy and compute-intensive application workloads.
Best suited for Online Analytics Processing (OLAP) transactions.
Supported Engines:
Redis: Offers advanced data structures, replication, persistence, and clustering.
Memcached: A simpler, multi-threaded caching solution ideal for large, horizontal scaling.
Scalability and Flexibility:
Push-button scalability for memory, writes, and reads.
Nodes can be easily added or removed to meet demand.
High Availability and Reliability:
Nodes are automatically replaced in case of failure.
Redis supports master/slave replication, automatic failover, and cross-AZ high availability.
Security and Control:
Access controlled via VPC security groups and subnet groups.
Nodes are not accessible from the Internet or across different VPCs.
Supports encryption in transit and at rest (for Redis).
Cost-Effective:
Billed based on node size and hours of use.
Options for on-demand or reserved instances (but not Spot instances).
Integration and Management:
Fully integrated with other AWS services.
Simplified management through the AWS Management Console, CLI, SDKs, and APIs.
Maintenance windows for software patching.

Use Cases:

Session Store: Store session data for web applications to provide a fast and reliable user experience.
Database Query Caching: Cache the results of frequently executed database queries to reduce database load and improve response times.
Computational Caching: Cache the results of computationally intensive operations to save resources and reduce processing times.
Leaderboards/Counting: Use Redis for storing real-time leaderboards and counters due to its advanced data structures.
Streaming Data: Utilize Redis for real-time data processing and analytics, leveraging its support for streams and other data types.
use cases of elasticache
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Column 2
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Use Case
Benefit
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Web session store
In cases with load-balanced web servers, store web session information in Redis so if a server is lost, the session info is not lost, and another web server can pick it up
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Database caching
Use Memcached in front of AWS RDS to cache popular queries to offload work from RDS and return results faster to users
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Leaderboards
Use Redis to provide a live leaderboard for millions of users of your mobile app
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Streaming data dashboards
Provide a landing spot for streaming sensor data on the factory floor, providing live real-time dashboard displays
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ElastiCache Architecture:

Nodes:
The smallest building block, each node is a fixed-size chunk of secure, network-attached RAM.
Runs an instance of either Memcached or Redis.
Each node has its own DNS name and port.
Clusters:
A collection of one or more nodes using the same caching engine.
Nodes within a cluster can span multiple subnets of the same subnet group.
Subnet Groups:
A collection of subnets designated for your ElastiCache clusters within a VPC.
Required for deploying ElastiCache in a VPC.
Endpoints:
Unique addresses used by applications to connect to ElastiCache nodes or clusters.

Maintenance and Updates:

Maintenance windows can be defined to allow software patching to occur.
ElastiCache automatically applies updates during these windows to ensure minimal disruption.

Engine Differences:

Memcached:
Simpler model with support for large nodes and multiple cores/threads.
Can easily scale in and out.
Ideal for caching objects and DB results.
Redis:
More complex model with support for encryption, replication, high availability, and backup/restore.
Supports advanced data structures, such as sorted sets and hashes.
Can be configured for cross-AZ replication and automatic failover.

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Exam tip: the key use cases for ElastiCache are offloading reads from a database and storing the results of computations and session state. Also, remember that ElastiCache is an in-memory database and it’s a managed service (so you can’t run it on EC2).



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