AWS Database Migration Service (Preview)

aws.amazon.com

49 points·runesoerensen··9 comments

Genuinely curious how it's possible to port things like triggers from one engine to the next, when they may have fundamentally different syntax and semantics.

That's been a "thing" for a while now. It's tricky, has some rough edges, but doable.

Neat. How does it work? Like, do they compile one system's triggers to some sort of intermediate language, and then compile that back to the target system's language?

Does the resulting code resemble something a human would write?

It's a combination of that (usually the intermediate language is ANSI SQL) and also used stored procs & UDT's to provide "work alike" behaviors.

Wonder if it's possible to use this to upgrade Amazon RDS instances?

At the moment you can't upgrade an existing postgres 9.3 RDS instance to 9.4 without dumping all the data and importing it into a new 9.4 RDS instance.

That's possible according to the page:

> AWS Database Migration Service can migrate on-premises databases to Amazon RDS or Amazon EC2, databases running on EC2 to RDS, or vice versa, as well as migrate an RDS database to another RDS database.

Excellent, will look forward to testing it out when it's available in eu-west-1. We'd like to use some of the new features in postgres 9.4 but our production DBs on RDS are stuck on 9.3 at the moment.

Sadly according to https://aws.amazon.com/dms/faqs/

RDS SQL Server, RDS Postgres, and ODBC sources are supported in bulk extract mode only; the change data capture mode (CDC) is not yet supported.

A shame since one of the biggest drawbacks to running postgres in RDS is getting the data out.

Does this help with online schema migrations too? Maybe for blue/green deployment of DB schema changes?

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