Re: refactoring relation extension and BufferAlloc(), faster COPY

Hi,

On 2023-01-20 13:40:55 +1300, David Rowley wrote:
> On Tue, 10 Jan 2023 at 15:08, Andres Freund <andres(at)anarazel(dot)de> wrote:
> > Thanks for letting me now. Updated version attached.
>
> I'm not too sure I've qualified for giving a meaningful design review
> here, but I have started looking at the patches and so far only made
> it as far as 0006.

Thanks!

> I noted down the following while reading:
>
> v2-0001:
>
> 1. BufferCheckOneLocalPin needs a header comment
>
> v2-0002:
>
> 2. The following comment and corresponding code to release the
> extension lock has been moved now.
>
> /*
> * Release the file-extension lock; it's now OK for someone else to extend
> * the relation some more.
> */
>
> I think it's worth detailing out why it's fine to release the
> extension lock in the new location. You've added detail to the commit
> message but I think you need to do the same in the comments too.

Will do.

> v2-0003
>
> 3. FileFallocate() and FileZero() should likely document what they
> return, i.e zero on success and non-zero on failure.

I guess I just tried to fit in with the rest of the file :)

> 4. I'm not quite clear on why you've modified FileGetRawDesc() to call
> FileAccess() twice.

I do not have the faintest idea what happened there... Will fix.

> v2-0004:
>
> 5. Is it worth having two versions of PinLocalBuffer() one to adjust
> the usage count and one that does not? Couldn't the version that does
> not adjust the count skip doing pg_atomic_read_u32()?

I think it'd be nicer to just move the read inside the if
(adjust_usagecount). That way the rest of the function doesn't have to be
duplicated.

Thanks,

Andres Freund