From 702d1b95831c1a34a217ad63b14895226962955a Mon Sep 17 00:00:00 2001 From: Kirill Smelkov Date: Sat, 10 Sep 2016 18:01:10 +0300 Subject: pack-objects: respect --local/--honor-pack-keep/--incremental when bitmap is in use Since 6b8fda2d (pack-objects: use bitmaps when packing objects) there are two codepaths in pack-objects: with & without using bitmap reachability index. However add_object_entry_from_bitmap(), despite its non-bitmapped counterpart add_object_entry(), in no way does check for whether --local or --honor-pack-keep or --incremental should be respected. In non-bitmapped codepath this is handled in want_object_in_pack(), but bitmapped codepath has simply no such checking at all. The bitmapped codepath however was allowing to pass in all those options and with bitmap indices still being used under such conditions - potentially giving wrong output (e.g. including objects from non-local or .keep'ed pack). We can easily fix this by noting the following: when an object comes to add_object_entry_from_bitmap() it can come for two reasons: 1. entries coming from main pack covered by bitmap index, and 2. object coming from, possibly alternate, loose or other packs. "2" can be already handled by want_object_in_pack() and to cover "1" we can teach want_object_in_pack() to expect that *found_pack can be non-NULL, meaning calling client already found object's pack entry. In want_object_in_pack() we care to start the checks from already found pack, if we have one, this way determining the answer right away in case neither --local nor --honour-pack-keep are active. In particular, as p5310-pack-bitmaps.sh shows (3 consecutive runs), we do not do harm to served-with-bitmap clones performance-wise: Test 56dfeb62 this tree ----------------------------------------------------------------- 5310.2: repack to disk 9.08(8.20+0.25) 9.09(8.14+0.32) +0.1% 5310.3: simulated clone 1.92(2.12+0.08) 1.93(2.12+0.09) +0.5% 5310.4: simulated fetch 0.82(1.07+0.04) 0.82(1.06+0.04) +0.0% 5310.6: partial bitmap 1.96(2.42+0.13) 1.95(2.40+0.15) -0.5% Test 56dfeb62 this tree ----------------------------------------------------------------- 5310.2: repack to disk 9.11(8.16+0.32) 9.11(8.19+0.28) +0.0% 5310.3: simulated clone 1.93(2.14+0.07) 1.92(2.11+0.10) -0.5% 5310.4: simulated fetch 0.82(1.06+0.04) 0.82(1.04+0.05) +0.0% 5310.6: partial bitmap 1.95(2.38+0.16) 1.94(2.39+0.14) -0.5% Test 56dfeb62 this tree ----------------------------------------------------------------- 5310.2: repack to disk 9.13(8.17+0.31) 9.07(8.13+0.28) -0.7% 5310.3: simulated clone 1.92(2.13+0.07) 1.91(2.12+0.06) -0.5% 5310.4: simulated fetch 0.82(1.08+0.03) 0.82(1.08+0.03) +0.0% 5310.6: partial bitmap 1.96(2.43+0.14) 1.96(2.42+0.14) +0.0% with delta timings showing they are all within noise from run to run. In the general case we do not want to call find_pack_entry_one() more than once, because it is expensive. This patch splits the loop in want_object_in_pack() into two parts: finding the object and seeing if it impacts our choice to include it in the pack. We may call the inexpensive want_found_object() twice, but we will never call find_pack_entry_one() if we do not need to. I appreciate help and discussing this change with Junio C Hamano and Jeff King. Signed-off-by: Kirill Smelkov Signed-off-by: Junio C Hamano --- t/t5310-pack-bitmaps.sh | 92 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 92 insertions(+) (limited to 't') diff --git a/t/t5310-pack-bitmaps.sh b/t/t5310-pack-bitmaps.sh index 3893afd687..a278d3032a 100755 --- a/t/t5310-pack-bitmaps.sh +++ b/t/t5310-pack-bitmaps.sh @@ -7,6 +7,18 @@ objpath () { echo ".git/objects/$(echo "$1" | sed -e 's|\(..\)|\1/|')" } +# show objects present in pack ($1 should be associated *.idx) +list_packed_objects () { + git show-index <"$1" | cut -d' ' -f2 +} + +# has_any pattern-file content-file +# tests whether content-file has any entry from pattern-file with entries being +# whole lines. +has_any () { + grep -Ff "$1" "$2" +} + test_expect_success 'setup repo with moderate-sized history' ' for i in $(test_seq 1 10); do test_commit $i @@ -16,6 +28,7 @@ test_expect_success 'setup repo with moderate-sized history' ' test_commit side-$i done && git checkout master && + bitmaptip=$(git rev-parse master) && blob=$(echo tagged-blob | git hash-object -w --stdin) && git tag tagged-blob $blob && git config repack.writebitmaps true && @@ -118,6 +131,71 @@ test_expect_success 'incremental repack can disable bitmaps' ' git repack -d --no-write-bitmap-index ' +test_expect_success 'pack-objects respects --local (non-local loose)' ' + git init --bare alt.git && + echo $(pwd)/alt.git/objects >.git/objects/info/alternates && + echo content1 >file1 && + # non-local loose object which is not present in bitmapped pack + altblob=$(GIT_DIR=alt.git git hash-object -w file1) && + # non-local loose object which is also present in bitmapped pack + git cat-file blob $blob | GIT_DIR=alt.git git hash-object -w --stdin && + git add file1 && + test_tick && + git commit -m commit_file1 && + echo HEAD | git pack-objects --local --stdout --revs >1.pack && + git index-pack 1.pack && + list_packed_objects 1.idx >1.objects && + printf "%s\n" "$altblob" "$blob" >nonlocal-loose && + ! has_any nonlocal-loose 1.objects +' + +test_expect_success 'pack-objects respects --honor-pack-keep (local non-bitmapped pack)' ' + echo content2 >file2 && + blob2=$(git hash-object -w file2) && + git add file2 && + test_tick && + git commit -m commit_file2 && + printf "%s\n" "$blob2" "$bitmaptip" >keepobjects && + pack2=$(git pack-objects pack2 .git/objects/pack/pack2-$pack2.keep && + rm $(objpath $blob2) && + echo HEAD | git pack-objects --honor-pack-keep --stdout --revs >2a.pack && + git index-pack 2a.pack && + list_packed_objects 2a.idx >2a.objects && + ! has_any keepobjects 2a.objects +' + +test_expect_success 'pack-objects respects --local (non-local pack)' ' + mv .git/objects/pack/pack2-$pack2.* alt.git/objects/pack/ && + echo HEAD | git pack-objects --local --stdout --revs >2b.pack && + git index-pack 2b.pack && + list_packed_objects 2b.idx >2b.objects && + ! has_any keepobjects 2b.objects +' + +test_expect_success 'pack-objects respects --honor-pack-keep (local bitmapped pack)' ' + ls .git/objects/pack/ | grep bitmap >output && + test_line_count = 1 output && + packbitmap=$(basename $(cat output) .bitmap) && + list_packed_objects .git/objects/pack/$packbitmap.idx >packbitmap.objects && + test_when_finished "rm -f .git/objects/pack/$packbitmap.keep" && + >.git/objects/pack/$packbitmap.keep && + echo HEAD | git pack-objects --honor-pack-keep --stdout --revs >3a.pack && + git index-pack 3a.pack && + list_packed_objects 3a.idx >3a.objects && + ! has_any packbitmap.objects 3a.objects +' + +test_expect_success 'pack-objects respects --local (non-local bitmapped pack)' ' + mv .git/objects/pack/$packbitmap.* alt.git/objects/pack/ && + test_when_finished "mv alt.git/objects/pack/$packbitmap.* .git/objects/pack/" && + echo HEAD | git pack-objects --local --stdout --revs >3b.pack && + git index-pack 3b.pack && + list_packed_objects 3b.idx >3b.objects && + ! has_any packbitmap.objects 3b.objects +' + test_expect_success 'full repack, reusing previous bitmaps' ' git repack -ad && ls .git/objects/pack/ | grep bitmap >output && @@ -143,6 +221,20 @@ test_expect_success 'create objects for missing-HAVE tests' ' EOF ' +test_expect_success 'pack-objects respects --incremental' ' + cat >revs2 <<-EOF && + HEAD + $commit + EOF + git pack-objects --incremental --stdout --revs 4.pack && + git index-pack 4.pack && + list_packed_objects 4.idx >4.objects && + test_line_count = 4 4.objects && + git rev-list --objects $commit >revlist && + cut -d" " -f1 revlist |sort >objects && + test_cmp 4.objects objects +' + test_expect_success 'pack with missing blob' ' rm $(objpath $blob) && git pack-objects --stdout --revs /dev/null -- cgit v1.2.3 From 645c432d6196903bcd9e8a82d150aac1428ccf34 Mon Sep 17 00:00:00 2001 From: Kirill Smelkov Date: Sat, 10 Sep 2016 18:01:44 +0300 Subject: pack-objects: use reachability bitmap index when generating non-stdout pack Starting from 6b8fda2d (pack-objects: use bitmaps when packing objects) if a repository has bitmap index, pack-objects can nicely speedup "Counting objects" graph traversal phase. That however was done only for case when resultant pack is sent to stdout, not written into a file. The reason here is for on-disk repack by default we want: - to produce good pack (with bitmap index not-yet-packed objects are emitted to pack in suboptimal order). - to use more robust pack-generation codepath (avoiding possible bugs in bitmap code and possible bitmap index corruption). Jeff King further explains: The reason for this split is that pack-objects tries to determine how "careful" it should be based on whether we are packing to disk or to stdout. Packing to disk implies "git repack", and that we will likely delete the old packs after finishing. We want to be more careful (so as not to carry forward a corruption, and to generate a more optimal pack), and we presumably run less frequently and can afford extra CPU. Whereas packing to stdout implies serving a remote via "git fetch" or "git push". This happens more frequently (e.g., a server handling many fetching clients), and we assume the receiving end takes more responsibility for verifying the data. But this isn't always the case. One might want to generate on-disk packfiles for a specialized object transfer. Just using "--stdout" and writing to a file is not optimal, as it will not generate the matching pack index. So it would be useful to have some way of overriding this heuristic: to tell pack-objects that even though it should generate on-disk files, it is still OK to use the reachability bitmaps to do the traversal. So we can teach pack-objects to use bitmap index for initial object counting phase when generating resultant pack file too: - if we take care to not let it be activated under git-repack: See above about repack robustness and not forward-carrying corruption. - if we know bitmap index generation is not enabled for resultant pack: The current code has singleton bitmap_git, so it cannot work simultaneously with two bitmap indices. We also want to avoid (at least with current implementation) generating bitmaps off of bitmaps. The reason here is: when generating a pack, not-yet-packed objects will be emitted into pack in suboptimal order and added to tail of the bitmap as "extended entries". When the resultant pack + some new objects in associated repository are in turn used to generate another pack with bitmap, the situation repeats: new objects are again not emitted optimally and just added to bitmap tail - not in recency order. So the pack badness can grow over time when at each step we have bitmapped pack + some other objects. That's why we want to avoid generating bitmaps off of bitmaps, not to let pack badness grow. - if we keep pack reuse enabled still only for "send-to-stdout" case: Because pack-to-file needs to generate index for destination pack, and currently on pack reuse raw entries are directly written out to the destination pack by write_reused_pack(), bypassing needed for pack index generation bookkeeping done by regular codepath in write_one() and friends. ( In the future we might teach pack-reuse code about cases when index also needs to be generated for resultant pack and remove pack-reuse-only-for-stdout limitation ) This way for pack-objects -> file we get nice speedup: erp5.git[1] (~230MB) extracted from ~ 5GB lab.nexedi.com backup repository managed by git-backup[2] via time echo 0186ac99 | git pack-objects --revs erp5pack before: 37.2s after: 26.2s And for `git repack -adb` packed git.git time echo 5c589a73 | git pack-objects --revs gitpack before: 7.1s after: 3.6s i.e. it can be 30% - 50% speedup for pack extraction. git-backup extracts many packs on repositories restoration. That was my initial motivation for the patch. [1] https://lab.nexedi.com/nexedi/erp5 [2] https://lab.nexedi.com/kirr/git-backup NOTE Jeff also suggests that pack.useBitmaps was probably a mistake to introduce originally. This way we are not adding another config point, but instead just always default to-file pack-objects not to use bitmap index: Tools which need to generate on-disk packs with using bitmap, can pass --use-bitmap-index explicitly. And git-repack does never pass --use-bitmap-index, so this way we can be sure regular on-disk repacking remains robust. NOTE2 `git pack-objects --stdout >file.pack` + `git index-pack file.pack` is much slower than `git pack-objects file.pack`. Extracting erp5.git pack from lab.nexedi.com backup repository: $ time echo 0186ac99 | git pack-objects --stdout --revs >erp5pack-stdout.pack real 0m22.309s user 0m21.148s sys 0m0.932s $ time git index-pack erp5pack-stdout.pack real 0m50.873s <-- more than 2 times slower than time to generate pack itself! user 0m49.300s sys 0m1.360s So the time for `pack-object --stdout >file.pack` + `index-pack file.pack` is 72s, while `pack-objects file.pack` which does both pack and index is 27s. And even `pack-objects --no-use-bitmap-index file.pack` is 37s. Jeff explains: The packfile does not carry the sha1 of the objects. A receiving index-pack has to compute them itself, including inflating and applying all of the deltas. that's why for `git-backup restore` we want to teach `git pack-objects file.pack` to use bitmaps instead of using `git pack-objects --stdout >file.pack` + `git index-pack file.pack`. NOTE3 The speedup is now tracked via t/perf/p5310-pack-bitmaps.sh Test 56dfeb62 this tree -------------------------------------------------------------------------------- 5310.2: repack to disk 8.98(8.05+0.29) 9.05(8.08+0.33) +0.8% 5310.3: simulated clone 2.02(2.27+0.09) 2.01(2.25+0.08) -0.5% 5310.4: simulated fetch 0.81(1.07+0.02) 0.81(1.05+0.04) +0.0% 5310.5: pack to file 7.58(7.04+0.28) 7.60(7.04+0.30) +0.3% 5310.6: pack to file (bitmap) 7.55(7.02+0.28) 3.25(2.82+0.18) -57.0% 5310.8: clone (partial bitmap) 1.83(2.26+0.12) 1.82(2.22+0.14) -0.5% 5310.9: pack to file (partial bitmap) 6.86(6.58+0.30) 2.87(2.74+0.20) -58.2% More context: http://marc.info/?t=146792101400001&r=1&w=2 http://public-inbox.org/git/20160707190917.20011-1-kirr@nexedi.com/T/#t Cc: Vicent Marti Helped-by: Jeff King Signed-off-by: Kirill Smelkov Signed-off-by: Junio C Hamano --- t/perf/p5310-pack-bitmaps.sh | 14 +++++++++++++- t/t5310-pack-bitmaps.sh | 12 ++++++++++++ 2 files changed, 25 insertions(+), 1 deletion(-) (limited to 't') diff --git a/t/perf/p5310-pack-bitmaps.sh b/t/perf/p5310-pack-bitmaps.sh index de2a224a36..bb91dbb173 100755 --- a/t/perf/p5310-pack-bitmaps.sh +++ b/t/perf/p5310-pack-bitmaps.sh @@ -32,6 +32,14 @@ test_perf 'simulated fetch' ' } | git pack-objects --revs --stdout >/dev/null ' +test_perf 'pack to file' ' + git pack-objects --all pack1 /dev/null +' + +test_perf 'pack to file (bitmap)' ' + git pack-objects --use-bitmap-index --all pack1b /dev/null +' + test_expect_success 'create partial bitmap state' ' # pick a commit to represent the repo tip in the past cutoff=$(git rev-list HEAD~100 -1) && @@ -53,8 +61,12 @@ test_expect_success 'create partial bitmap state' ' git update-ref HEAD $orig_tip ' -test_perf 'partial bitmap' ' +test_perf 'clone (partial bitmap)' ' git pack-objects --stdout --all /dev/null ' +test_perf 'pack to file (partial bitmap)' ' + git pack-objects --use-bitmap-index --all pack2b /dev/null +' + test_done diff --git a/t/t5310-pack-bitmaps.sh b/t/t5310-pack-bitmaps.sh index a278d3032a..9602e9af67 100755 --- a/t/t5310-pack-bitmaps.sh +++ b/t/t5310-pack-bitmaps.sh @@ -196,6 +196,18 @@ test_expect_success 'pack-objects respects --local (non-local bitmapped pack)' ' ! has_any packbitmap.objects 3b.objects ' +test_expect_success 'pack-objects to file can use bitmap' ' + # make sure we still have 1 bitmap index from previous tests + ls .git/objects/pack/ | grep bitmap >output && + test_line_count = 1 output && + # verify equivalent packs are generated with/without using bitmap index + packasha1=$(git pack-objects --no-use-bitmap-index --all packa packa.objects && + list_packed_objects packb.objects && + test_cmp packa.objects packb.objects +' + test_expect_success 'full repack, reusing previous bitmaps' ' git repack -ad && ls .git/objects/pack/ | grep bitmap >output && -- cgit v1.2.3