From: Jeff King <peff@peff.net>
To: Jonathan Tan <jonathantanmy@google.com>
Cc: git@vger.kernel.org
Subject: Re: [PATCH 2/2] index-pack: prefetch missing REF_DELTA bases
Date: Thu, 16 May 2019 21:22:34 -0400 [thread overview]
Message-ID: <20190517012234.GA31027@sigill.intra.peff.net> (raw)
In-Reply-To: <20190517010950.GA30146@sigill.intra.peff.net>
On Thu, May 16, 2019 at 09:09:50PM -0400, Jeff King wrote:
> - will we ever append a presumed-thin base to the pack, only to later
> realize that we already have that object, creating a duplicate
> object in the pack? If so, do we handle this correctly when
> generating the index (I know we've had issues in the past and have
> expressly forbidden duplicates from appearing in the index; even
> having a duplicate in the pack stream itself is non-ideal, though,
> as it screws up things like on-disk size calculations).
>
> Because of the sorting in fix_unresolved_deltas(), I think this
> could easily be prevented if the non-thin delta is OFS_DELTA (by
> just checking for the base in our already-found list of objects
> before we call read_object_file(). But for REF_DELTA, I think we
> have no way of knowing that appending is the wrong thing (and no
> good way of backing it out afterwards).
Actually, I think even for REF_DELTA our pack-objects would never
produce such a pack, because IIRC we _always_ put bases in the pack
before their deltas. But that's a pretty subtle thing to depend on. I'm
fine with it if violating it just means things are slightly less
optimal. I'm more worried if it means that index-pack silently produces
a bogus pack.
I think to trigger it you'd have to manually assemble an evil pack as I
described (e.g., using the routines in t/lib-pack.sh). I'm going offline
for a bit, but I may have a go at it later tonight or tomorrow.
-Peff
next prev parent reply other threads:[~2019-05-17 1:22 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
2019-05-17 1:09 ` Jeff King
2019-05-17 1:22 ` Jeff King [this message]
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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