Re: [PATCH] cleanup hashindex for pg_migrator hashindex compat mode (for 8.4)

Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Tue, May 26, 2009 at 10:09 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> I don't trust filterdiff one bit :-(

> For any particular reason, or just natural skepticism?

IIRC it was demonstrated to be broken the last time it was proposed
as a solution to our problems. Maybe it's been fixed since then, but
I don't have any confidence in it, since evidently it's not been stress
tested very hard.

> I believe there have been some wild-eyed claims tossed around in this
> space previously that unified diffs don't provide all the same
> information as context diffs, which is flatly false.

No, the gripe has always been just that they're less readable for
nontrivial changes.

> The not-so-nice thing about unified diffs is that when there is a huge
> hunk of code that's changed, there are probably by chance a few
> identical lines buried in there, like " }", so the + and - lines
> end up mixed together in a way that wouldn't happen in a context diff
> (which would turn the whole thing into two big "!" sections). It's no
> problem for a machine to understand this, but it's hard to read for a
> human being.

Exactly. Even without identical lines, I find that the old and new code
gets intermixed in easily-confusing ways. -u is very readable for
isolated single-line changes, but for anything larger, not so much.

regards, tom lane