Re: [PATCH] revision.c: reduce object database queries

[Junio C Hamano <gitster@pobox.com>]

Jeff King <peff@peff.net> writes:

>> This code comes originally form 454fbbcde3 (git-rev-list: allow missing
>> objects when the parent is marked UNINTERESTING, 2005-07-10). But later,
>> in aeeae1b771 (revision traversal: allow UNINTERESTING objects to be
>> missing, 2009-01-27), we marked dealt with calling parse_object() on the
>> parents more directly.
>>
>> So what I wonder is whether this code is simply redundant and can go
>> away entirely. That would save the has_object_file() call in all cases.

Hmm, interesting. I forgot all what I did around this area, but you
are right.  

> There's a similar case for trees. ...
> though technically the existing code allows _missing_ trees, but
> not on corrupt ones.

True, but the intention of these "do not care too much about missing
stuff while marking uninteresting" effort is aligned better with
ignoring corrupt ones, too, I would think, as "missing" in that
sentence is in fact about "not availble", and stuff that exists in
corrupt form is still not available anyway.  So I do not think it
makes a bad change to start allowing corrupt ones.

> I guess this is perhaps less interesting, because we only mark trees
> directly fed from the pending array, not every tree of commits that we
> traverse. Though if you had a really gigantic tree, it might be
> measurable.

I tend to agree that this is less interesting case than commits.

A huge tree with millions of entries in a single level would spend
quite a lot of cycle in slurping the tree data to in-core buffer,
but we do not actually parse these million entries upon opening the
tree, so it may not be too bad.