Re: [RFC] Incremental backup v2: add backup profile to base backup

On Fri, Oct  3, 2014 at 06:08:47PM +0200, Marco Nenciarini wrote:
> >> Any comment will be appreciated. In particular I'd appreciate comments
> >> on correctness of relnode files detection and LSN extraction code.
> > 
> > I didn't look at it in detail, but one future problem comes to mind:
> > Once you implement the server-side code that only sends a file if its
> > LSN is higher than the cutoff point that the client gave, you'll have to
> > scan the whole file first, to see if there are any blocks with a higher
> > LSN. At least until you find the first such block. So with a file-level
> > implementation of this sort, you'll have to scan all files twice, in the
> > worst case.
> > 
> 
> It's true. To solve this you have to keep a central maxLSN directory,
> but I think it introduces more issues than it solves.

The central issue Heikki is pointing out is whether we should implement
a file-based system if we already know that a block-based system will be
superior in every way.  I agree with that and agree that implementing
just file-based isn't worth it as we would have to support it forever.

So, in summary, if you target just a file-based system, be prepared that
it might be rejected.

--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com
 + Everyone has their own god. +