Re: block-level incremental backup

On Fri, Aug 9, 2019 at 6:36 PM Robert Haas <robertmhaas(at)gmail(dot)com> wrote:

> On Wed, Aug 7, 2019 at 5:46 AM Jeevan Chalke
> <jeevan(dot)chalke(at)enterprisedb(dot)com> wrote:
> > So, do you mean we should just do fread() and fwrite() for the whole
> file?
> >
> > I thought it is better if it was done by the OS itself instead of
> reading 1GB
> > into the memory and writing the same to the file.
>
> Well, 'cp' is just a C program. If they can write code to copy a
> file, so can we, and then we're not dependent on 'cp' being installed,
> working properly, being in the user's path or at the hard-coded
> pathname we expect, etc. There's an existing copy_file() function in
> src/backed/storage/file/copydir.c which I'd probably look into
> adapting for frontend use. I'm not sure whether it would be important
> to adapt the data-flushing code that's present in that routine or
> whether we could get by with just the loop to read() and write() data.
>

Agree that we can certainly use open(), read(), write(), and close() here,
but
given that pg_basebackup.c and basbackup.c are using file operations, I
think
using fopen(), fread(), fwrite(), and fclose() will be better here, at-least
for consistetncy.

Let me know if we still want to go with native OS calls.

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

--
Jeevan Chalke
Technical Architect, Product Development
EnterpriseDB Corporation
The Enterprise PostgreSQL Company