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From: Jeff King <>
To: Jonathan Tan <>
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: <> (raw)
In-Reply-To: <>

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/ I'm going offline
for a bit, but I may have a go at it later tonight or tomorrow.


  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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