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You mean pg_upgrade?

http://www.postgresql.org/docs/9.5/static/pgupgrade.html

pg_upgrade is a pretty reasonable compromise, but it would be nice if an upgrade didn't require your entire database be taken offline for the duration. I can install a new MS SQL Server instance, attach a database from the old instance and be going in under a minute of downtime - this is literally the only pain point I have with Pq, but considering I don't typically upgrade EVERY release (I still have 9.4 instances that have no reason to be upgraded to 9.5 since the applications aren't in-house) it's not typically a huge deal.

pg_upgrade in link mode typically takes less than a minute to run unless you have a lot of tables; the runtime is dependant on the number of database objects, not rows or size of the database.

Database statistics are not preserved across pg_upgrade so you'll have to run ANALYZE on the database after the upgrade which may take a while as it usually needs to read all or almost all of your data.

I just recently upgraded a ~1 TB database, the actual upgrade process took less than a minute but analyzing it took much longer.

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