Re: pg_upgrade and rsync

On Mon, Jan 26, 2015 at 05:41:59PM -0500, Stephen Frost wrote:
> I've thought about it a fair bit actually and I agree that there is some
> risk to using rsync for *incremental* base backups.  That is, you have
> a setup where you loop with:
> 
> pg_start_backup
> rsync -> dest
> pg_stop_backup
> 
> without using -I, changing what 'dest' is, or making sure it's empty
> every time.  The problem is the 1s-level granularity used on the
> timestamp.  A possible set of operations, all within 1s, is:
> 
> file changed
> rsync starts copying the file
> file changed again (somewhere prior to where rsync is at)
> rsync finishes the file copy
> 
> Now, this isn't actually a problem for the first time that file is
> backed up- the issue is if that file isn't changed again.  rsync won't
> re-copy it, but that change that rsync missed won't be in the WAL
> history for the *second* backup that's done (only the first), leading to
> a case where that file would end up corrupted.

Interesting problem, but doesn't rsync use sub-second accuracy?

--  Bruce Momjian          http://momjian.us EnterpriseDB                             http://enterprisedb.com
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