| commit | 795006fff45fb2b5e92be0121f92a876c409a1a3 | [log] [tgz] |
|---|---|---|
| author | Patrick Steinhardt <ps@pks.im> | Mon Apr 15 08:41:25 2024 +0200 |
| committer | Junio C Hamano <gitster@pobox.com> | Mon Apr 15 10:42:00 2024 -0700 |
| tree | 23b0eb4a141552655af52db08e27c560572d6968 | |
| parent | 97d1f233c6e06dac978b419506a2bf1038f71eaf [diff] |
pack-bitmap: gracefully handle missing BTMP chunks In 0fea6b73f1 (Merge branch 'tb/multi-pack-verbatim-reuse', 2024-01-12) we have introduced multi-pack verbatim reuse of objects. This series has introduced a new BTMP chunk, which encodes information about bitmapped objects in the multi-pack index. Starting with dab60934e3 (pack-bitmap: pass `bitmapped_pack` struct to pack-reuse functions, 2023-12-14) we use this information to figure out objects which we can reuse from each of the packfiles. One thing that we glossed over though is backwards compatibility with repositories that do not yet have BTMP chunks in their multi-pack index. In that case, `nth_bitmapped_pack()` would return an error, which causes us to emit a warning followed by another error message. These warnings are visible to users that fetch from a repository: ``` $ git fetch ... remote: error: MIDX does not contain the BTMP chunk remote: warning: unable to load pack: 'pack-f6bb7bd71d345ea9fe604b60cab9ba9ece54ffbe.idx', disabling pack-reuse remote: Enumerating objects: 40, done. remote: Counting objects: 100% (40/40), done. remote: Compressing objects: 100% (39/39), done. remote: Total 40 (delta 5), reused 0 (delta 0), pack-reused 0 (from 0) ... ``` While the fetch succeeds the user is left wondering what they did wrong. Furthermore, as visible both from the warning and from the reuse stats, pack-reuse is completely disabled in such repositories. What is quite interesting is that this issue can even be triggered in case `pack.allowPackReuse=single` is set, which is the default value. One could have expected that in this case we fall back to the old logic, which is to use the preferred packfile without consulting BTMP chunks at all. But either we fail with the above error in case they are missing, or we use the first pack in the multi-pack-index. The former case disables pack-reuse altogether, whereas the latter case may result in reusing objects from a suboptimal packfile. Fix this issue by partially reverting the logic back to what we had before this patch series landed. Namely, in the case where we have no BTMP chunks or when `pack.allowPackReuse=single` are set, we use the preferred pack instead of consulting the BTMP chunks. Helped-by: Taylor Blau <me@ttaylorr.com> Signed-off-by: Patrick Steinhardt <ps@pks.im> Signed-off-by: Junio C Hamano <gitster@pobox.com>
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