Re: Correct comment in RemoveNonParentXlogFiles()

At Wed, 3 Aug 2022 18:16:33 +0530, Ashutosh Sharma <ashu(dot)coek88(at)gmail(dot)com> wrote in
> Following comment in RemoveNonParentXlogFiles() says that we are trying to
> remove any WAL file whose segment number is >= the segment number of the
> first WAL file on the new timeline. However, looking at the code, I can say
> that we are trying to remove the WAL files from the previous timeline whose
> segment number is just greater than (not equal to) the segment number of
> the first WAL file in the new timeline. I think we should improve this
> comment, thoughts?
>
> /*
> * Remove files that are on a timeline older than the new one we're
> * switching to, but with a segment number >= the first segment on
> the
> * new timeline.
> */
> if (strncmp(xlde->d_name, switchseg, 8) < 0 &&
> strcmp(xlde->d_name + 8, switchseg + 8) > 0)

I'm not sure I'm fully getting your point. The current comment is
correctly saying that it removes the segments "on a timeline older
than the new one". I agree about segment comparison.

So, if I changed that comment, I would finish with the following change.

- * switching to, but with a segment number >= the first segment on
+ * switching to, but with a segment number greater than the first segment on

That disagreement started at the time the code was introduced by
b2a5545bd6. Leaving the last segment in the old timeline is correct
since it is renamed to .partial later. If timeline switch happened
just at segment boundary, that segment would not not be created.

regards.

--
Kyotaro Horiguchi
NTT Open Source Software Center