Re: BUG #19776: pg_combinebackup ignores the truncation_block_length of an intermediate incremental backup

Hi Sai Pranav,

> - Nothing tests the full_copy_possible = false in the new block: with that
> line removed, the whole suite still passes. I think the line is needed,
> though: without it, a chain where no block comes from an incremental file
> and the full file happens to be as long as the latest
> truncation_block_length would be copied whole, including the blocks the
> intermediate backup had truncated away. I couldn't build that case through
> the server (regrowing the relation writes blocks that end up in the later
> incremental file), so a test may not be practical. A short comment saying
> why the line is there would help.
>
> - Small wording nit in the new comment: blocks at or beyond an incremental
> file's truncation_block_length are not necessarily blocks that "did not
> exist at the time of this backup"; they may have been truncated away at
> some point during that backup's WAL range. Something like "Blocks at or
> beyond this file's truncation_block_length were truncated away at some
> point before this backup, so their contents in any earlier backup are
> stale" might be clearer.

Thanks for reviewing and testing the patch! Both points make sense.
I updated the comment in v3 to clarify the truncation wording and
explain why we also clear full_copy_possible there.

Regards,
Rajesh