git-internals-and-the-object-model-module

TOP CONCEPTS

commit objectType-3 git object containing tree SHA, parent SHA(s), author, committer, timestamp, and message; forms the his

tree entry modeOctal mode in tree object: 100644 (regular file), 100755 (executable), 040000 (subtree), 120000 (symlink), 160

tree objectType-2 git object listing directory entries as (mode, name, sha1) tuples; represents a single directory snapsh

ref pointerNamed file under .git/refs/ containing a SHA-1; represents a branch tip, tag, or remote-tracking branch; updat

blob objectType-1 git object storing raw file contents verbatim; identified by SHA-1 of content; no filename or metadata

sha1 hash160-bit cryptographic hash computed over object content; serves as object's unique addressable name in git's c

delta compressionGit's storage optimization encoding an object as a series of copy/insert commands relative to a base object; O

object databaseDirectory-backed key-value store under .git/objects/; loose objects stored as zlib-deflated files keyed by SHA

reachabilityProperty of an object being transitively accessible from another; defines ancestry in the commit DAG; basis fo

author fieldName and email in commit object identifying primary creator; distinct from committer who applied the patch.

commit graphBinary file .git/objects/info/commit-graph storing commit reachability, generation numbers, and bloom filter d

mode type bitsThe upper bits of the octal mode identifying the entry's object category: regular file, directory, symlink, or

object type inspectiongit cat-file -t reveals object type; git cat-file -s shows byte size; git cat-file -p pretty-prints content; g

commit message encoding encoding valueThe character encoding name stored in the encoding header (UTF-8, ISO-8859-1, Windows-1252, etc.); controls by

commit message encoding transcoding logicgit's internal conversion from the stored encoding_value to the requested log_encoding_flag encoding; uses ico

packfileSingle binary file consolidating many objects via delta compression; named pack-*.pack with companion .idx ind

submodule pointerEntry in a parent repository's tree object referencing a specific commit of a nested repository; stored as mod

maintenance taskgit maintenance subcommand scheduling background optimization: gc, commit-graph rebuild, incremental-repack, p

partial cloneClone with --filter omitting blob objects from transfer; missing blobs retrieved on demand via fetch-object; e

tag objectType-4 git object wrapping another object with a tag name, tagger info, and message; typically used for annota