Re: [PATCH] pg_upgrade: support for btrfs copy-on-write clones

On Fri, Oct 4, 2013 at 10:42:46PM +0300, Oskari Saarenmaa wrote:
> Thanks for the offers, but it looks like ZFS doesn't actually implement
> a similar file level clone operation. See
> https://github.com/zfsonlinux/zfs/issues/405 for discussion on a feature
> request for it.
>
> ZFS does support cloning entire datasets which seem to be similar to
> btrfs subvolume snapshots and could be used to set up a new data
> directory for a new $PGDATA. This would require the original $PGDATA
> to be a dataset/subvolume of its own and quite a bit different logic
> (than just another file copy method in pg_upgrade) to initialize the new
> version's $PGDATA as a snapshot/clone of the original. The way this
> would work is that the original $PGDATA dataset/subvolume gets cloned to
> a new location after which we move the files out of the way of the new
> PG installation and run pg_upgrade in link mode. I'm not sure if
> there's a good way to integrate this into pg_upgrade or if it's just
> something that could be documented as a fast way to run pg_upgrade
> without touching original files.
>
> With btrfs tooling the sequence would be something like this:
>
> btrfs subvolume snapshot /srv/pg92 /srv/pg93
> mv /srv/pg93/data /srv/pg93/data92
> initdb /data/pg93/data
> pg_upgrade --link \
> --old-datadir=/data/pg93/data92 \
> --new-datadir=/data/pg93/data

Does btrfs support file system snapshots? If so, shouldn't people just
take a snapshot of the old data directory before the ugprade, rather
than using cloning?

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

+ It's impossible for everything to be true. +