Re: finding changed blocks using WAL scanning

On Mon, Apr 15, 2019 at 4:31 PM Bruce Momjian <bruce(at)momjian(dot)us> 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.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company