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@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com
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