{
    "mode": "man",
    "parameter": "gitformat-commit-graph",
    "section": "5",
    "url": "https://www.chedong.com/phpMan.php/man/gitformat-commit-graph/5/json",
    "generated": "2026-11-08T13:31:55Z",
    "synopsis": "$GITDIR/objects/info/commit-graph\n$GITDIR/objects/info/commit-graphs/*",
    "sections": {
        "NAME": {
            "content": "gitformat-commit-graph - Git commit-graph format\n",
            "subsections": []
        },
        "SYNOPSIS": {
            "content": "$GITDIR/objects/info/commit-graph\n$GITDIR/objects/info/commit-graphs/*\n\n",
            "subsections": []
        },
        "DESCRIPTION": {
            "content": "The Git commit-graph stores a list of commit OIDs and some associated metadata, including:\n\n•   The generation number of the commit.\n\n•   The root tree OID.\n\n•   The commit date.\n\n•   The parents of the commit, stored using positional references within the graph file.\n\n•   The Bloom filter of the commit carrying the paths that were changed between the commit\nand its first parent, if requested.\n\nThese positional references are stored as unsigned 32-bit integers corresponding to the array\nposition within the list of commit OIDs. Due to some special constants we use to track\nparents, we can store at most (1 << 30) + (1 << 29) + (1 << 28) - 1 (around 1.8 billion)\ncommits.\n\nCOMMIT-GRAPH FILES HAVE THE FOLLOWING FORMAT:\nIn order to allow extensions that add extra data to the graph, we organize the body into\n\"chunks\" and provide a binary lookup table at the beginning of the body. The header includes\ncertain values, such as number of chunks and hash type.\n\nAll multi-byte numbers are in network byte order.\n",
            "subsections": [
                {
                    "name": "HEADER:",
                    "content": "4-byte signature:\nThe signature is: {'C', 'G', 'P', 'H'}\n\n1-byte version number:\nCurrently, the only valid version is 1.\n\n1-byte Hash Version\nWe infer the hash length (H) from this value:\n1 => SHA-1\n2 => SHA-256\nIf the hash type does not match the repository's hash algorithm, the\ncommit-graph file should be ignored with a warning presented to the\nuser.\n\n1-byte number (C) of \"chunks\"\n\n1-byte number (B) of base commit-graphs\nWe infer the length (H*B) of the Base Graphs chunk\nfrom this value.\n"
                },
                {
                    "name": "CHUNK LOOKUP:",
                    "content": "(C + 1) * 12 bytes listing the table of contents for the chunks:\nFirst 4 bytes describe the chunk id. Value 0 is a terminating label.\nOther 8 bytes provide the byte-offset in current file for chunk to\nstart. (Chunks are ordered contiguously in the file, so you can infer\nthe length using the next chunk position if necessary.) Each chunk\nID appears at most once.\n\nThe CHUNK LOOKUP matches the table of contents from\nthe chunk-based file format, see linkgit:gitformat-chunk[5]\n\nThe remaining data in the body is described one chunk at a time, and\nthese chunks may be given in any order. Chunks are required unless\notherwise specified.\n"
                },
                {
                    "name": "CHUNK DATA:",
                    "content": "OID Fanout (ID: {O, I, D, F}) (256 * 4 bytes)\n\nThe ith entry, F[i], stores the number of OIDs with first\nbyte at most i. Thus F[255] stores the total\nnumber of commits (N).\n\nOID Lookup (ID: {O, I, D, L}) (N * H bytes)\n\nThe OIDs for all commits in the graph, sorted in ascending order.\n\nCommit Data (ID: {C, D, A, T }) (N * (H + 16) bytes)\n\n•   The first H bytes are for the OID of the root tree.\n\n•   The next 8 bytes are for the positions of the first two parents of the ith commit.\nStores value 0x70000000 if no parent in that position. If there are more than two\nparents, the second value has its most-significant bit on and the other bits store an\narray position into the Extra Edge List chunk.\n\n•   The next 8 bytes store the topological level (generation number v1) of the commit and\nthe commit time in seconds since EPOCH. The generation number uses the higher 30 bits\nof the first 4 bytes, while the commit time uses the 32 bits of the second 4 bytes,\nalong with the lowest 2 bits of the lowest byte, storing the 33rd and 34th bit of the\ncommit time.\n\nGeneration Data (ID: {G, D, A, 2 }) (N * 4 bytes) [Optional]\n\n•   This list of 4-byte values store corrected commit date offsets for the commits,\narranged in the same order as commit data chunk.\n\n•   If the corrected commit date offset cannot be stored within 31 bits, the value has\nits most-significant bit on and the other bits store the position of corrected commit\ndate into the Generation Data Overflow chunk.\n\n•   Generation Data chunk is present only when commit-graph file is written by compatible\nversions of Git and in case of split commit-graph chains, the topmost layer also has\nGeneration Data chunk.\n"
                },
                {
                    "name": "Generation Data Overflow (ID: {G, D, O, 2 }) [Optional]",
                    "content": "•   This list of 8-byte values stores the corrected commit date offsets for commits with\ncorrected commit date offsets that cannot be stored within 31 bits.\n\n•   Generation Data Overflow chunk is present only when Generation Data chunk is present\nand atleast one corrected commit date offset cannot be stored within 31 bits.\n"
                },
                {
                    "name": "Extra Edge List (ID: {E, D, G, E}) [Optional]",
                    "content": "This list of 4-byte values store the second through nth parents for\nall octopus merges. The second parent value in the commit data stores\nan array position within this list along with the most-significant bit\non. Starting at that array position, iterate through this list of commit\npositions for the parents until reaching a value with the most-significant\nbit on. The other bits correspond to the position of the last parent.\n\nBloom Filter Index (ID: {B, I, D, X}) (N * 4 bytes) [Optional]\n\n•   The ith entry, BIDX[i], stores the number of bytes in all Bloom filters from commit 0\nto commit i (inclusive) in lexicographic order. The Bloom filter for the i-th commit\nspans from BIDX[i-1] to BIDX[i] (plus header length), where BIDX[-1] is 0.\n\n•   The BIDX chunk is ignored if the BDAT chunk is not present.\n"
                },
                {
                    "name": "Bloom Filter Data (ID: {B, D, A, T}) [Optional]",
                    "content": "•   It starts with header consisting of three unsigned 32-bit integers:\n\n•   Version of the hash algorithm being used. We currently only support value 1 which\ncorresponds to the 32-bit version of the murmur3 hash implemented exactly as\ndescribed in https://en.wikipedia.org/wiki/MurmurHash#Algorithm and the double\nhashing technique using seed values 0x293ae76f and 0x7e646e2 as described in\nhttps://doi.org/10.1007/978-3-540-30494-426 \"Bloom Filters in Probabilistic\nVerification\"\n\n•   The number of times a path is hashed and hence the number of bit positions that\ncumulatively determine whether a file is present in the commit.\n\n•   The minimum number of bits b per entry in the Bloom filter. If the filter\ncontains n entries, then the filter size is the minimum number of 64-bit words\nthat contain n*b bits.\n\n•   The rest of the chunk is the concatenation of all the computed Bloom filters for the\ncommits in lexicographic order.\n\n•   Note: Commits with no changes or more than 512 changes have Bloom filters of length\none, with either all bits set to zero or one respectively.\n\n•   The BDAT chunk is present if and only if BIDX is present.\n"
                },
                {
                    "name": "Base Graphs List (ID: {B, A, S, E}) [Optional]",
                    "content": "This list of H-byte hashes describe a set of B commit-graph files that\nform a commit-graph chain. The graph position for the ith commit in this\nfile's OID Lookup chunk is equal to i plus the number of commits in all\nbase graphs.  If B is non-zero, this chunk must exist.\n"
                },
                {
                    "name": "TRAILER:",
                    "content": "H-byte HASH-checksum of all of the above.\n\nHISTORICAL NOTES:\nThe Generation Data (GDA2) and Generation Data Overflow (GDO2) chunks have the number 2 in\ntheir chunk IDs because a previous version of Git wrote possibly erroneous data in these\nchunks with the IDs \"GDAT\" and \"GDOV\". By changing the IDs, newer versions of Git will\nsilently ignore those older chunks and write the new information without trusting the\nincorrect data.\n"
                }
            ]
        },
        "GIT": {
            "content": "Part of the git(1) suite\n\nGit 2.43.0                                   07/02/2025                    GITFORMAT-COMMIT-GRAPH(5)",
            "subsections": []
        }
    },
    "summary": "gitformat-commit-graph - Git commit-graph format",
    "flags": [],
    "examples": [],
    "see_also": []
}