Thread: code cleanups

Some modest cleanups I've accumulated.

Justin Pryzby <pryzby@telsasoft.com> writes:
> Some modest cleanups I've accumulated.

Hmm ...

I don't especially care for either 0001 or 0002, mainly because
I do not agree that this is good style:

-    bool        nulls[PG_STAT_GET_RECOVERY_PREFETCH_COLS];
+    bool        nulls[PG_STAT_GET_RECOVERY_PREFETCH_COLS] = {0};

It causes the code to be far more in bed than I like with the assumption
that we're initializing to physical zeroes.  The explicit loop method
can be trivially adjusted to initialize to "true" or some other value;
at least for bool arrays, that's true of memset'ing as well.  But this,
if you decide you need something other than zeroes, is a foot-gun.
In particular, someone whose C is a bit weak might mistakenly think that

    bool        nulls[PG_STAT_GET_RECOVERY_PREFETCH_COLS] = {true};

will set all the array elements to true.  Nor is there a plausible
argument that this is more efficient.  So I don't care for this approach
and I don't want to adopt it.

0003: I agree with getting rid of the duplicated code, but did you go
far enough?  Isn't the code just above those parent checks also pretty
redundant?  It would be more intellectually consistent to move the full
responsibility for setting acl_ok into a subroutine.  This shows in
the patch as you have it because the header comment for
recheck_parent_acl is completely out-of-context.

0004: Right, somebody injected code in a poorly chosen place
(yet another victim of the "add at the end" anti-pattern).

0005: No particular objection, but it's not much of an improvement
either.  It seems maybe a shade less consistent with the following
line.

0006: These changes will cause fetching of one more source byte than
was fetched before.  I'm not sure that's safe, so I don't think this
is an improvement.

            regards, tom lane

On Wed, Nov 23, 2022 at 12:53 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> at least for bool arrays, that's true of memset'ing as well.  But this,
> if you decide you need something other than zeroes, is a foot-gun.
> In particular, someone whose C is a bit weak might mistakenly think that
>
>         bool            nulls[PG_STAT_GET_RECOVERY_PREFETCH_COLS] = {true};
>
> will set all the array elements to true.  Nor is there a plausible
> argument that this is more efficient.  So I don't care for this approach
> and I don't want to adopt it.

I don't really know what the argument is for the explicit initializer
style, but I think this argument against it is pretty weak.

It should be more than fine to assume that anyone who is hacking on
PostgreSQL is proficient in C. It's true that there might be some
people who aren't, or who aren't familiar with the limitations of the
initializer construct, and I include myself in that latter category. I
don't think it was part of C when I learned C. But if we don't possess
the collective expertise as a project to bring people who have missed
these details of the C programming language up to speed, we should
just throw in the towel now and go home.

Hacking on PostgreSQL is HARD and it relies on knowing FAR more than
just the basics of how to code in C. Put differently, if you can't
even figure out how C works, you have no chance of doing anything very
interesting with the PostgreSQL code base, because you're going to
have to figure out a lot more than the basics of the implementation
language to make a meaningful contribution.

-- 
Robert Haas
EDB: http://www.enterprisedb.com