På tirsdag 06. februar 2018 kl. 01:09:18, skrev David Fetter <
david@fetter.org>:
Folks,
While chatting with Bruce about how to make something better than
pg_upgrade, we (and by "we," I mean mostly Bruce) came up with the
following.
What needs improvement:
- pg_upgrade forces a down time event, no matter how cleverly it's done.
- pg_upgrade is very much a blocker for on-disk format changes.
The proposal:
- Add a new script--possibly Perl or Bash, which would:
- Initdb a new cluster with the new version of PostgreSQL and a
different port.
- Start logical replication from the old version to the new
version.
- Poll until a pre-determined default amount of replication lag was observed, then:
* Issue an ALTER SYSTEM on the new server to change its port to the old server's
* Issue a pg_ctl stop -w to the old server
* Issue a pg_ctl restart on the new server
* Happiness!
Assumptions underlying it:
- Disk and similar resources are cheap enough for most users that
doubling up during the upgrade is feasible.
- The default upgrade path should require exactly one step.
- Errors do not, by and large, have the capacity to violate an SLA.
The proposal has blockers:
- We don't actually have logical decoding for DDL, although I'm given
to understand that Álvaro Herrera has done some yeoman follow-up
work on Dimitri Fontaine's PoC patches.
- We don't have logical decoding for DCL (GRANT/REVOKE)
- Need to add support for decoding LargeObjects.
