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Actually we're on postgres... It just makes me nervous when the migration is taking upwards of 10 minutes to complete since some of our tables have millions of rows and lots of concurrent read/writes are happening.

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I don't think executing long-running DDL with concurrent read/writes is that bad, especially if the DDL is additive and doesn't lock the whole table.

Concurrency - isn't that what a DB is supposed to do well?

If the site isn't taken down during an update, some parts of it will always be broken during a schema migration since our ORM expects each table corresponding to a data model to be in sync after a code update. I guess you could always version your data models and handle the pre-upgrade and post-upgrade cases, but that seems like a lot of work in our situation.

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