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When we use pack bitmaps rather than walking the object graph, we end up with the list of objects to include in the packfile, but we do not know the path at which any tree or blob objects would be found. In a recently packed repository, this is fine. A fetch would use the paths only as a heuristic in the delta compression phase, and a fully packed repository should not need to do much delta compression. As time passes, though, we may acquire more objects on top of our large bitmapped pack. If clients fetch frequently, then they never even look at the bitmapped history, and all works as usual. However, a client who has not fetched since the last bitmap repack will have "have" tips in the bitmapped history, but "want" newer objects. The bitmaps themselves degrade gracefully in this circumstance. We manually walk the more recent bits of history, and then use bitmaps when we hit them. But we would also like to perform delta compression between the newer objects and the bitmapped objects (both to delta against what we know the user already has, but also between "new" and "old" objects that the user is fetching). The lack of pathnames makes our delta heuristics much less effective. This patch adds an optional cache of the 32-bit name_hash values to the end of the bitmap file. If present, a reader can use it to match bitmapped and non-bitmapped names during delta compression. Here are perf results for p5310: Test origin/master HEAD^ HEAD ------------------------------------------------------------------------------------------------- 5310.2: repack to disk 36.81(37.82+1.43) 47.70(48.74+1.41) +29.6% 47.75(48.70+1.51) +29.7% 5310.3: simulated clone 30.78(29.70+2.14) 1.08(0.97+0.10) -96.5% 1.07(0.94+0.12) -96.5% 5310.4: simulated fetch 3.16(6.10+0.08) 3.54(10.65+0.06) +12.0% 1.70(3.07+0.06) -46.2% 5310.6: partial bitmap 36.76(43.19+1.81) 6.71(11.25+0.76) -81.7% 4.08(6.26+0.46) -88.9% You can see that the time spent on an incremental fetch goes down, as our delta heuristics are able to do their work. And we save time on the partial bitmap clone for the same reason. Signed-off-by: Vicent Marti <tanoku@gmail.com> Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
65 lines
1.8 KiB
C
65 lines
1.8 KiB
C
#ifndef PACK_BITMAP_H
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#define PACK_BITMAP_H
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#include "ewah/ewok.h"
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#include "khash.h"
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#include "pack-objects.h"
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struct bitmap_disk_entry {
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uint32_t object_pos;
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uint8_t xor_offset;
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uint8_t flags;
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} __attribute__((packed));
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struct bitmap_disk_header {
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char magic[4];
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uint16_t version;
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uint16_t options;
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uint32_t entry_count;
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unsigned char checksum[20];
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};
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static const char BITMAP_IDX_SIGNATURE[] = {'B', 'I', 'T', 'M'};
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#define NEEDS_BITMAP (1u<<22)
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enum pack_bitmap_opts {
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BITMAP_OPT_FULL_DAG = 1,
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BITMAP_OPT_HASH_CACHE = 4,
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};
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enum pack_bitmap_flags {
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BITMAP_FLAG_REUSE = 0x1
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};
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typedef int (*show_reachable_fn)(
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const unsigned char *sha1,
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enum object_type type,
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int flags,
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uint32_t hash,
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struct packed_git *found_pack,
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off_t found_offset);
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int prepare_bitmap_git(void);
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void count_bitmap_commit_list(uint32_t *commits, uint32_t *trees, uint32_t *blobs, uint32_t *tags);
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void traverse_bitmap_commit_list(show_reachable_fn show_reachable);
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void test_bitmap_walk(struct rev_info *revs);
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char *pack_bitmap_filename(struct packed_git *p);
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int prepare_bitmap_walk(struct rev_info *revs);
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int reuse_partial_packfile_from_bitmap(struct packed_git **packfile, uint32_t *entries, off_t *up_to);
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int rebuild_existing_bitmaps(struct packing_data *mapping, khash_sha1 *reused_bitmaps, int show_progress);
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void bitmap_writer_show_progress(int show);
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void bitmap_writer_set_checksum(unsigned char *sha1);
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void bitmap_writer_build_type_index(struct pack_idx_entry **index, uint32_t index_nr);
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void bitmap_writer_reuse_bitmaps(struct packing_data *to_pack);
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void bitmap_writer_select_commits(struct commit **indexed_commits,
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unsigned int indexed_commits_nr, int max_bitmaps);
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void bitmap_writer_build(struct packing_data *to_pack);
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void bitmap_writer_finish(struct pack_idx_entry **index,
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uint32_t index_nr,
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const char *filename,
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uint16_t options);
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#endif
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