what is sql?

what is nosql?

what is cap theorem?

The CAP theorem states that any networked shared-data system can have at most two of three desirable properties:

• consistency (C) equivalent to having a single up-to-date copy of the data (linearizable);
• high availability (A) of that data (system always accepts updates);
• and tolerance to network partitions (P)

Ref:

• An Illustrated Proof of the CAP Theorem
• https://www.infoq.com/articles/cap-twelve-years-later-how-the-rules-have-changed/

compare rds multi az instance and multi az cluster.

• Multi AZ Instance:

  • 1 Primary instance
  • 1 Standby replica:
    • can’t be used for reads / write 👈 not for performance scaling, only for availability
    • kept in sync Synchronously with the primary instance

• Multi AZ Cluster:

  • 1 Writer DB instance
  • 2 Reader DB instances:
    • can be used for read 👈 limited read scaling
    • kept in sync Asynchronously with the Writer instance 👈 replication lag (aka Replica lag)

what kind of backups does rds support?

RDS support 2 kind of backup:

• Manually Snapshots
• Automated Backups

what is rds manually snapshot?

A backup performed manually and live past the termination of an RDS instance

what is rds automated backups?

Backups performed automatically by RDS:

• 0 to 35 days retention.
• RDS also use S3 to store transaction logs every 5 minutes.

👉 With RDS Automated Backups, RPO can be only 5 minutes. 💪

where is a rds snapshot restored to?

RDS Snapshot is restored to a new RDS instance, with new address.

how long is an rds restore?

RDS Restores aren’t fast. Be careful with RTO.

what is the impact of rds read-replicas to rpo/rto?

Read-Replicas offer:

• near 0 RPO.
• very low RTO 👈 RRs can be promoted quickly.

can read-replicas solve data corruption?

No. Data corruption will be replicated to RRs.

how long is aurora global database's replication between regions?

Less than or equal 1s

why use rds proxy?

• Opening/Closing DB Connections consume resources.

  • Increase latency.
  • Especially with serverless architecture.

• Handling failure of DB instance is hard:

  • Doing it within application add risks

👉 RDS Proxy solves these problems.

how rds proxy works?

Amazon RDS Proxy:

• sits between your application and your relational database
• to efficiently manage connections to the database

👉 improve scalability of the application.

can dms be used for on-premises db?

Yes and No.

• DMS can be used to migrate from/to on-premises DB if the other endpoint were on AWS.
• If both endpoints are on-premise, DMS can NOT be used.

where is dms run?

On a replication instance (an EC2 instance).

which part of dms really run the migration?

DMS Task:

• Full load
• Full load + CDC
• CDC only

aws schema conversion tool (sct) vs aws dms schema conversion?

• AWS Schema Conversion Tool (SCT):

  • convert your existing database schema from one database engine to another.
  • used to convert data warehouse schemas, big data frameworks, application SQL code, and ETL processes.

• AWS DMS Schema Conversion:

  • a web-version of the AWS SCT. [1]
  • supports less database platforms and provides more limited functionality compared