Re: finding changed blocks using WAL scanning

On Mon, Apr 15, 2019 at 09:04:13PM -0400, Robert Haas wrote:
> On Mon, Apr 15, 2019 at 4:31 PM Bruce Momjian  wrote:
> > Can I throw out a simple idea?  What if, when we finish writing a WAL
> > file, we create a new file 000000010000000000000001.modblock which
> > lists all the heap/index files and block numbers modified in that WAL
> > file?  How much does that help with the list I posted earlier?
> >
> >         I think there is some interesting complexity brought up in this thread.
> >         Which options are going to minimize storage I/O, network I/O, have only
> >         background overhead, allow parallel operation, integrate with
> >         pg_basebackup.  Eventually we will need to evaluate the incremental
> >         backup options against these criteria.
> >
> > I am thinking tools could retain modblock files along with WAL, could
> > pull full-page-writes from WAL, or from PGDATA.  It avoids the need to
> > scan 16MB WAL files, and the WAL files and modblock files could be
> > expired independently.
> 
> That is pretty much exactly what I was intending to propose.

OK, good.  Some of your wording was vague so I was unclear exactly what
you were suggesting.

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

+ As you are, so once was I.  As I am, so you will be. +
+                      Ancient Roman grave inscription +