From: Jonathan Tan <jonathantanmy@google.com>
To: peff@peff.net
Cc: jonathantanmy@google.com, git@vger.kernel.org
Subject: Re: [PATCH 2/2] index-pack: prefetch missing REF_DELTA bases
Date: Thu, 16 May 2019 16:15:09 -0700 [thread overview]
Message-ID: <20190516231509.253998-1-jonathantanmy@google.com> (raw)
In-Reply-To: <20190516214257.GD10787@sigill.intra.peff.net>
> > > Right, REF_DELTA is definitely correctly handled currently, and I don't
> > > think that would break with your patch. It's just that your patch would
> > > introduce a bunch of extra traffic as we request bases separately that
> > > are already in the pack.
> >
> > Ah...I see. For this problem, I think that it can be solved with the
> > "if (objects[d->obj_no].real_type != OBJ_REF_DELTA)" check that the
> > existing code uses before calling read_object(). I'll include this in
> > the next reroll if any other issue comes up.
>
> I'm confused about this. Aren't we pre-fetching before we've actually
> resolved deltas? The base could be in the pack as a true base, and we
> might have seen it already then. But it could itself be a delta, and we
> wouldn't know we have it until we resolve it (this gets into the
> lucky/unlucky ordering thing).
resolve_deltas(), invoked before any new code introduced in this patch,
has this comment:
> /*
> * Second pass:
> * - for all non-delta objects, look if it is used as a base for
> * deltas;
> * - if used as a base, uncompress the object and apply all deltas,
> * recursively checking if the resulting object is used as a base
> * for some more deltas.
> */
I haven't seen any code that contradicts this comment. And looking at
the code, for each non-delta object, I think that all deltas are checked
- regardless of whether they appear before or after that non-delta
object. (find_ref_delta() does a binary search from 0 to
nr_ref_deltas, calculated in parse_pack_objects() which happens before
any resolution of deltas.)
And find_unresolved_deltas_1() (called from resolve_deltas() indirectly)
sets the real_type when it resolves a delta, as far as I can tell.
So there is more than one "resolve deltas" step - resolve_deltas() and
then fix_unresolved_deltas(). The pre-fetching happens only during the
latter.
next prev parent reply other threads:[~2019-05-16 23:15 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-14 21:10 [PATCH 0/2] Partial clone fix: handling received REF_DELTA Jonathan Tan
2019-05-14 21:10 ` [PATCH 1/2] t5616: refactor packfile replacement Jonathan Tan
2019-05-15 8:36 ` Johannes Schindelin
2019-05-15 18:22 ` Jonathan Tan
2019-05-14 21:10 ` [PATCH 2/2] index-pack: prefetch missing REF_DELTA bases Jonathan Tan
2019-05-15 8:46 ` Johannes Schindelin
2019-05-15 18:28 ` Jonathan Tan
2019-05-17 18:33 ` Johannes Schindelin
2019-05-15 23:16 ` Jeff King
2019-05-16 1:43 ` Junio C Hamano
2019-05-16 4:04 ` Jeff King
2019-05-16 18:26 ` Jonathan Tan
2019-05-16 21:12 ` Jeff King
2019-05-16 21:30 ` Jonathan Tan
2019-05-16 21:42 ` Jeff King
2019-05-16 23:15 ` Jonathan Tan [this message]
2019-05-17 1:09 ` Jeff King
2019-05-17 1:22 ` Jeff King
2019-05-17 4:39 ` Jeff King
2019-05-17 4:42 ` Jeff King
2019-05-17 7:20 ` Duy Nguyen
2019-05-17 8:55 ` Jeff King
2019-05-18 11:39 ` Duy Nguyen
2019-05-20 23:04 ` Nicolas Pitre
2019-05-21 21:20 ` Jeff King
2019-06-03 22:23 ` Jonathan Nieder
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