diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/config/pack.txt | 7 | ||||
| -rw-r--r-- | Documentation/technical/bitmap-format.txt | 39 |
2 files changed, 46 insertions, 0 deletions
diff --git a/Documentation/config/pack.txt b/Documentation/config/pack.txt index 3e581eab84..53093d9996 100644 --- a/Documentation/config/pack.txt +++ b/Documentation/config/pack.txt @@ -164,6 +164,13 @@ When writing a multi-pack reachability bitmap, no new namehashes are computed; instead, any namehashes stored in an existing bitmap are permuted into their appropriate location when writing a new bitmap. +pack.writeBitmapLookupTable:: + When true, Git will include a "lookup table" section in the + bitmap index (if one is written). This table is used to defer + loading individual bitmaps as late as possible. This can be + beneficial in repositories that have relatively large bitmap + indexes. Defaults to false. + pack.writeReverseIndex:: When true, git will write a corresponding .rev file (see: linkgit:gitformat-pack[5]) diff --git a/Documentation/technical/bitmap-format.txt b/Documentation/technical/bitmap-format.txt index a85f58f515..c2e652b71a 100644 --- a/Documentation/technical/bitmap-format.txt +++ b/Documentation/technical/bitmap-format.txt @@ -72,6 +72,17 @@ MIDXs, both the bit-cache and rev-cache extensions are required. pack/MIDX. The format and meaning of the name-hash is described below. + ** {empty} + BITMAP_OPT_LOOKUP_TABLE (0x10): ::: + If present, the end of the bitmap file contains a table + containing a list of `N` <commit_pos, offset, xor_row> + triplets. The format and meaning of the table is described + below. ++ +NOTE: Unlike the xor_offset used to compress an individual bitmap, +`xor_row` stores an *absolute* index into the lookup table, not a location +relative to the current entry. + 4-byte entry count (network byte order): :: The total count of entries (bitmapped commits) in this bitmap index. @@ -216,3 +227,31 @@ Note that this hashing scheme is tied to the BITMAP_OPT_HASH_CACHE flag. If implementations want to choose a different hashing scheme, they are free to do so, but MUST allocate a new header flag (because comparing hashes made under two different schemes would be pointless). + +Commit lookup table +------------------- + +If the BITMAP_OPT_LOOKUP_TABLE flag is set, the last `N * (4 + 8 + 4)` +bytes (preceding the name-hash cache and trailing hash) of the `.bitmap` +file contains a lookup table specifying the information needed to get +the desired bitmap from the entries without parsing previous unnecessary +bitmaps. + +For a `.bitmap` containing `nr_entries` reachability bitmaps, the table +contains a list of `nr_entries` <commit_pos, offset, xor_row> triplets +(sorted in the ascending order of `commit_pos`). The content of i'th +triplet is - + + * {empty} + commit_pos (4 byte integer, network byte order): :: + It stores the object position of a commit (in the midx or pack + index). + + * {empty} + offset (8 byte integer, network byte order): :: + The offset from which that commit's bitmap can be read. + + * {empty} + xor_row (4 byte integer, network byte order): :: + The position of the triplet whose bitmap is used to compress + this one, or `0xffffffff` if no such bitmap exists. |