Re: file cloning in pg_upgrade and CREATE DATABASE

On Mon, Mar 19, 2018 at 04:14:15PM +0900, Michael Paquier wrote:
> Two other things I have noticed as well:
> 1) src/bin/pg_rewind/copy_fetch.c could benefit from similar speed-ups I
> think when copying data from source to target using the local mode of
> pg_rewind.  This could really improve cases where new relations are
> added after a promotion.
> 2) XLogFileCopy() uses a copy logic as well.  For large segments things
> could be improved, however we need to be careful about filling in the
> end of segments with zeros.

I have been thinking about this patch over the night, and here is a list
of bullet points which would be nice to tackle:
- Remove the current diff in copydir.
- Extend copy_file so as it is able to use fcopyfile.
- Move the work done in pg_upgrade into a common API which can as well
be used by pg_rewind as well.  One place would be to have a
frontend-only API in src/common which does the leg work.  I would
recommend working only on file descriptors as well for consistency with
copy_file_range.
- Add proper wait events for the backend calls.  Those are missing for
copy_file_range and copyfile.
- For XLogFileCopy, the problem may be trickier as the tail of a segment
is filled with zeroes, so dropping it from the first version of the
patch sounds wiser.

Patch is switched as waiting on author, I have set myself as a
reviewer.

Thanks,
--
Michael