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I'm talking about serious systematic migrations, not upgrades. In these instances, it is impossible to avoid downtime ( whether it be a few seconds, minutes or

I'm talking about serious systematic migrations, not upgrades. In these instances, it is impossible to avoid downtime ( whether it be a few seconds, minutes or even hours ). It's one of the reasons why SLAs do not offer 100% uptimes.

theptip 9y ago
Interested in a concrete example of where you see a migration being impossible without downtime; I'm not aware of Amazon or Google taking their APIs down for maintenance, which suggests that you can solve these problems with enough engineering spend. > depending on... how coupled everything is If you're just saying here that some systems aren't currently able to migrate in a hitless way, rather than claiming that it would never be possible for some systems, then I fully agree. Hitless migrations require a lot of work, and probably aren't worth the cost for many applications/systems.
- stickfigure 9y ago
  Neither Amazon nor Google run off of an RDBMS. Relational databases are awesome, but it's much harder to achieve 100% uptime compared to schemaless, distributed, replicated data stores. You easily can take down your system with one innocuous-looking DDL migration that works great in test but grinds the machine to a halt on a production dataset.
  - theptip 9y ago
    That's a good general point, but Youtube does use MySQL: https://www.mysql.com/customers/view/?id=750 https://www.mysql.com/customers/view/?id=750 http://highscalability.com/youtube-architecture http://highscalability.com/youtube-architecture