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

From: Junio C Hamano <gitster@pobox.com>
Date: Feb 27, 2018, 23:16 UTC
Message-ID: <xmqqefl6nhud.fsf@gitster-ct.c.googlers.com>
In-Reply-To: <20180226013822.GA9385@sigill.intra.peff.net>

Jeff King <peff@peff.net> writes:

Show 8 quoted lines

>> 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.