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I am planning to migrate my 300GB RDS PostgreSql database to Aurora MySql using SCT and DMS. RDS Postgresql is in seven regions in current setup. Datapipelines are used to ingest data in these instances and keep them in sync. I was thinking that once I create global database in one region, I will be able to add secondary instances in six other regions. But, I read that global instances support just one additional secondary region.

The only relevant benefits for global database from the docs are:

  • Having an additional secondary instance will have faster replication compared to having a read replica.
  • Faster disaster recovery as the secondary instance can be promoted to primary under a minute.

Now I am wondering what is the difference between:

  1. Having a Aurora global database in one region with writer and reader, adding a secondary region, adding five read replicas(from primary or secondary)

  2. Having a Aurora regional database (with a writer and reader) and adding six read replicas.

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  • Did you ever find the answer to this, I'm wondering the same? Overall what are the advantages of using a global database as opposed to creating a read replica in another region. Nov 1, 2019 at 11:54

2 Answers 2

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Aurora uses MySQL replication to replicate to a secondary data while Aurora Global database uses underlying hardware to replicate your data from another region which doesn't affect your database performance compared to using read replicas.

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  • I'm at 2021 AWS re:Invent and per SysBench OLTP (write-only) testing, the replication performance is incredible versus logical replication since storage is decoupled from compute and the cross-region log copy is done on AWS high speed backbone. There is a negligable performance impact on the primary DB cluster during replication.
    – WEBjuju
    Nov 29, 2021 at 19:03
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From aws faq

Physical replication, called Aurora Global Database, uses dedicated infrastructure that leaves your databases entirely available to serve your application, and can replicate to up to five secondary regions with typical latency of under a second. It's available for both Aurora MySQL and Aurora PostgreSQL. For low-latency global reads and disaster recovery, we recommend using Aurora Global Database.

Aurora supports native logical replication in each database engine (binlog for MySQL and PostgreSQL replication slots for PostgreSQL), so you can replicate to Aurora and non-Aurora databases, even across regions.

Aurora MySQL also offers an easy-to-use logical cross-region read replica feature that supports up to five secondary AWS regions. It is based on single threaded MySQL binlog replication, so the replication lag will be influenced by the change/apply rate and delays in network communication between the specific regions selected.

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