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Diffstat (limited to 'Documentation/technical/index-format.txt')
| -rw-r--r-- | Documentation/technical/index-format.txt | 75 |
1 files changed, 61 insertions, 14 deletions
diff --git a/Documentation/technical/index-format.txt b/Documentation/technical/index-format.txt index f9a3644711..65da0daaa5 100644 --- a/Documentation/technical/index-format.txt +++ b/Documentation/technical/index-format.txt @@ -26,7 +26,7 @@ Git index format Extensions are identified by signature. Optional extensions can be ignored if Git does not understand them. - Git currently supports cached tree and resolve undo extensions. + Git currently supports cache tree and resolve undo extensions. 4-byte extension signature. If the first byte is 'A'..'Z' the extension is optional and can be ignored. @@ -44,6 +44,13 @@ Git index format localization, no special casing of directory separator '/'). Entries with the same name are sorted by their stage field. + An index entry typically represents a file. However, if sparse-checkout + is enabled in cone mode (`core.sparseCheckoutCone` is enabled) and the + `extensions.sparseIndex` extension is enabled, then the index may + contain entries for directories outside of the sparse-checkout definition. + These entries have mode `040000`, include the `SKIP_WORKTREE` bit, and + the path ends in a directory separator. + 32-bit ctime seconds, the last time a file's metadata changed this is stat(2) data @@ -136,14 +143,35 @@ Git index format == Extensions -=== Cached tree - - Cached tree extension contains pre-computed hashes for trees that can - be derived from the index. It helps speed up tree object generation - from index for a new commit. - - When a path is updated in index, the path must be invalidated and - removed from tree cache. +=== Cache tree + + Since the index does not record entries for directories, the cache + entries cannot describe tree objects that already exist in the object + database for regions of the index that are unchanged from an existing + commit. The cache tree extension stores a recursive tree structure that + describes the trees that already exist and completely match sections of + the cache entries. This speeds up tree object generation from the index + for a new commit by only computing the trees that are "new" to that + commit. It also assists when comparing the index to another tree, such + as `HEAD^{tree}`, since sections of the index can be skipped when a tree + comparison demonstrates equality. + + The recursive tree structure uses nodes that store a number of cache + entries, a list of subnodes, and an object ID (OID). The OID references + the existing tree for that node, if it is known to exist. The subnodes + correspond to subdirectories that themselves have cache tree nodes. The + number of cache entries corresponds to the number of cache entries in + the index that describe paths within that tree's directory. + + The extension tracks the full directory structure in the cache tree + extension, but this is generally smaller than the full cache entry list. + + When a path is updated in index, Git invalidates all nodes of the + recursive cache tree corresponding to the parent directories of that + path. We store these tree nodes as being "invalid" by using "-1" as the + number of cache entries. Invalid nodes still store a span of index + entries, allowing Git to focus its efforts when reconstructing a full + cache tree. The signature for this extension is { 'T', 'R', 'E', 'E' }. @@ -174,7 +202,8 @@ Git index format first entry represents the root level of the repository, followed by the first subtree--let's call this A--of the root level (with its name relative to the root level), followed by the first subtree of A (with - its name relative to A), ... + its name relative to A), and so on. The specified number of subtrees + indicates when the current level of the recursive stack is complete. === Resolve undo @@ -251,14 +280,14 @@ Git index format - Stat data of $GIT_DIR/info/exclude. See "Index entry" section from ctime field until "file size". - - Stat data of core.excludesfile + - Stat data of core.excludesFile - 32-bit dir_flags (see struct dir_struct) - Hash of $GIT_DIR/info/exclude. A null hash means the file does not exist. - - Hash of core.excludesfile. A null hash means the file does + - Hash of core.excludesFile. A null hash means the file does not exist. - NUL-terminated string of per-dir exclude file name. This usually @@ -306,12 +335,18 @@ The remaining data of each directory block is grouped by type: The extension starts with - - 32-bit version number: the current supported version is 1. + - 32-bit version number: the current supported versions are 1 and 2. - - 64-bit time: the extension data reflects all changes through the given + - (Version 1) + 64-bit time: the extension data reflects all changes through the given time which is stored as the nanoseconds elapsed since midnight, January 1, 1970. + - (Version 2) + A null terminated string: an opaque token defined by the file system + monitor application. The extension data reflects all changes relative + to that token. + - 32-bit bitmap size: the size of the CE_FSMONITOR_VALID bitmap. - An ewah bitmap, the n-th bit indicates whether the n-th index entry @@ -357,3 +392,15 @@ The remaining data of each directory block is grouped by type: in this block of entries. - 32-bit count of cache entries in this block + +== Sparse Directory Entries + + When using sparse-checkout in cone mode, some entire directories within + the index can be summarized by pointing to a tree object instead of the + entire expanded list of paths within that tree. An index containing such + entries is a "sparse index". Index format versions 4 and less were not + implemented with such entries in mind. Thus, for these versions, an + index containing sparse directory entries will include this extension + with signature { 's', 'd', 'i', 'r' }. Like the split-index extension, + tools should avoid interacting with a sparse index unless they understand + this extension. |