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Terry Parker dbd05433ec Move reachability checker generation into the ObjectReader object
Reachability checkers are retrieved from RevWalk and ObjectWalk objects:
* RevWalk.createReachabilityChecker()
* ObjectWalk.createObjectReachabilityChecker()

Since RevWalks and ObjectWalks are themselves directly instantiated
in hundreds of places (e.g. UploadPack...) overriding them in a
consistent way requires overloading 100s of methods, which isn't
feasible. Moving reachability checker generation to a more central
place solves that problem.

The ObjectReader object seems a good place from which to get
reachability checkers, because reachability checkers return
information about relationships between objects. ObjectDatabases
delegate many operations to ObjectReaders, and reachability bitmaps
are attached to ObjectReaders.

The Bitmapped and Pedestrian reachability checker objects were
package private in the org.eclipse.jgit.revwalk package. This change
makes them public and moves them to the
org.eclipse.jgit.internal.revwalk package. Corresponding tests are
also moved.

Motivation:
1) Reachability checking algorithms need to scale. One of the
   internal Android repositories has ~2.4 million refs/changes/*
   references, causing bad long tail performance in reachability
   checks.
2) Reachability check performance is impacted by repository
   topography: number of refs, number of objects, amounts of
   related vs. unrelated history.
3) Reachability check performance is also affected by per-branch
   access (Gerrit branch permissions) since different users can
   see different branches.
4) Reachability check performance isn't affected by any state in a
   RevWalk or ObjectWalk.

I don't yet know if a single algorithm will work for all cases in #2
and #3. We may need to evolve the ReachabilityChecker interfaces
over time to solve the Gerrit branch permissions case, or use
Gerrit-specific identity information to solve that in an efficient
way.

This change takes the existing public API and moves it to the
ObjectReader/whole repository level, which is where we can do
consistent customizations for #2 and #3. We intend to upstream the
best of whatever works, but anticipate the need for multiple rounds
of experimentation.

Change-Id: I9185feff43551fb387957c436112d5250486833d
Signed-off-by: Terry Parker <tparker@google.com>
2021-01-28 22:17:26 -08:00
.mvn Configure max heap size for Maven build 2016-12-09 11:02:10 +01:00
.settings Add resource preferences for top level jgit project 2019-12-16 11:20:12 +01:00
Documentation Fix formatting of config option values 2020-10-26 11:26:42 -04:00
lib Add org.eclipse.jetty.util.ajax to target platform and bazel deps 2021-01-12 10:14:42 +01:00
org.eclipse.jgit Move reachability checker generation into the ObjectReader object 2021-01-28 22:17:26 -08:00
org.eclipse.jgit.ant Prepare 5.11.0-SNAPSHOT builds 2020-12-02 15:57:16 +01:00
org.eclipse.jgit.ant.test Prepare 5.11.0-SNAPSHOT builds 2020-12-02 15:57:16 +01:00
org.eclipse.jgit.archive Prepare 5.11.0-SNAPSHOT builds 2020-12-02 15:57:16 +01:00
org.eclipse.jgit.benchmarks Update maven-shade-plugin to 3.2.4 2020-12-24 15:57:15 +01:00
org.eclipse.jgit.coverage Prepare 5.11.0-SNAPSHOT builds 2020-12-02 15:57:16 +01:00
org.eclipse.jgit.gpg.bc GPG user ID matching: use case-insensitive matching 2020-12-29 10:15:20 +01:00
org.eclipse.jgit.gpg.bc.test GPG user ID matching: use case-insensitive matching 2020-12-29 10:15:20 +01:00
org.eclipse.jgit.http.apache Correct the minimum required version of Apache httpclient 2021-01-18 16:18:09 +01:00
org.eclipse.jgit.http.server Prepare 5.11.0-SNAPSHOT builds 2020-12-02 15:57:16 +01:00
org.eclipse.jgit.http.test Correct the minimum required version of Apache httpclient 2021-01-18 16:18:09 +01:00
org.eclipse.jgit.junit Prepare 5.11.0-SNAPSHOT builds 2020-12-02 15:57:16 +01:00
org.eclipse.jgit.junit.http Use Map interface instead of ConcurrentHashMap class 2021-01-01 12:49:05 -05:00
org.eclipse.jgit.junit.ssh Client-side protocol V2 support for fetching 2021-01-01 21:22:30 +01:00
org.eclipse.jgit.lfs Correct the minimum required version of Apache httpclient 2021-01-18 16:18:09 +01:00
org.eclipse.jgit.lfs.server Correct the minimum required version of Apache httpclient 2021-01-18 16:18:09 +01:00
org.eclipse.jgit.lfs.server.test Correct the minimum required version of Apache httpclient 2021-01-18 16:18:09 +01:00
org.eclipse.jgit.lfs.test Prepare 5.11.0-SNAPSHOT builds 2020-12-02 15:57:16 +01:00
org.eclipse.jgit.packaging Add target platform for eclipse 4.19 staging 2021-01-12 23:26:09 +01:00
org.eclipse.jgit.pgm pgm: add missing dependency to org.apache.commons.logging 2021-01-17 18:04:38 -05:00
org.eclipse.jgit.pgm.test Prepare 5.11.0-SNAPSHOT builds 2020-12-02 15:57:16 +01:00
org.eclipse.jgit.ssh.apache Client-side protocol V2 support for fetching 2021-01-01 21:22:30 +01:00
org.eclipse.jgit.ssh.apache.test Client-side protocol V2 support for fetching 2021-01-01 21:22:30 +01:00
org.eclipse.jgit.ssh.jsch Client-side protocol V2 support for fetching 2021-01-01 21:22:30 +01:00
org.eclipse.jgit.ssh.jsch.test Client-side protocol V2 support for fetching 2021-01-01 21:22:30 +01:00
org.eclipse.jgit.test Move reachability checker generation into the ObjectReader object 2021-01-28 22:17:26 -08:00
org.eclipse.jgit.ui Prepare 5.11.0-SNAPSHOT builds 2020-12-02 15:57:16 +01:00
tools Bazel: Add workspace status command to stamp final artifact 2020-07-17 01:10:15 +02:00
.bazelrc Bazel: Add workspace status command to stamp final artifact 2020-07-17 01:10:15 +02:00
.bazelversion Bazel: Allow to build and run the tests with JDK 15 2020-11-28 23:29:41 +01:00
.gitattributes Initial JGit contribution to eclipse.org 2009-09-29 16:47:03 -07:00
.gitignore .gitignore: remove editor- and OS-specific files 2019-04-01 13:38:00 -07:00
.mailmap Update .mailmap 2018-09-25 19:03:22 -04:00
BUILD [Java 11] Remove dependency on javax.xml.bind package 2019-06-18 02:22:21 +02:00
CONTRIBUTING.md Update SUBMITTING_PATCHES 2014-07-20 17:44:53 -04:00
LICENSE Clean up LICENSE file 2010-07-02 14:52:49 -07:00
README.md Update README 2019-02-19 08:34:38 +09:00
WORKSPACE Update orbit to S20210105214148 and com.google.gson to 2.8.6 2021-01-12 23:26:09 +01:00
pom.xml Update orbit to S20210105214148 and com.google.gson to 2.8.6 2021-01-12 23:26:09 +01:00

README.md

Java Git

An implementation of the Git version control system in pure Java.

This project is licensed under the EDL (Eclipse Distribution License).

JGit can be imported straight into Eclipse and built and tested from there. It can be built from the command line using Maven or Bazel. The CI builds use Maven and run on Jenkins.

  • org.eclipse.jgit

    A pure Java library capable of being run standalone, with no additional support libraries. It provides classes to read and write a Git repository and operate on a working directory.

    All portions of JGit are covered by the EDL. Absolutely no GPL, LGPL or EPL contributions are accepted within this package.

  • org.eclipse.jgit.ant

    Ant tasks based on JGit.

  • org.eclipse.jgit.archive

    Support for exporting to various archive formats (zip etc).

  • org.eclipse.jgit.http.apache

    Apache httpclient support.

  • org.eclipse.jgit.http.server

    Server for the smart and dumb Git HTTP protocol.

  • org.eclipse.jgit.lfs

    Support for LFS (Large File Storage).

  • org.eclipse.jgit.lfs.server

    Basic LFS server support.

  • org.eclipse.jgit.packaging

    Production of Eclipse features and p2 repository for JGit. See the JGit Wiki on why and how to use this module.

  • org.eclipse.jgit.pgm

    Command-line interface Git commands implemented using JGit ("pgm" stands for program).

  • org.eclipse.jgit.ssh.apache

    Client support for the ssh protocol based on Apache Mina sshd.

  • org.eclipse.jgit.ui

    Simple UI for displaying git log.

Tests

  • org.eclipse.jgit.junit, org.eclipse.jgit.junit.http, org.eclipse.jgit.junit.ssh: Helpers for unit testing
  • org.eclipse.jgit.ant.test: Unit tests for org.eclipse.jgit.ant
  • org.eclipse.jgit.http.test: Unit tests for org.eclipse.jgit.http.server
  • org.eclipse.jgit.lfs.server.test: Unit tests for org.eclipse.jgit.lfs.server
  • org.eclipse.jgit.lfs.test: Unit tests for org.eclipse.jgit.lfs
  • org.eclipse.jgit.pgm.test: Unit tests for org.eclipse.jgit.pgm
  • org.eclipse.jgit.ssh.apache.test: Unit tests for org.eclipse.jgit.ssh.apache
  • org.eclipse.jgit.test: Unit tests for org.eclipse.jgit

Warnings/Caveats

  • Native symbolic links are supported, provided the file system supports them. For Windows you must use a non-administrator account and have the SeCreateSymbolicLinkPrivilege.

  • Only the timestamp of the index is used by JGit if the index is dirty.

  • JGit requires at least a Java 8 JDK.

  • CRLF conversion is performed depending on the core.autocrlf setting, however Git for Windows by default stores that setting during installation in the "system wide" configuration file. If Git is not installed, use the global or repository configuration for the core.autocrlf setting.

  • The system wide configuration file is located relative to where C Git is installed. Make sure Git can be found via the PATH environment variable. When installing Git for Windows check the "Run Git from the Windows Command Prompt" option. There are other options like Eclipse settings that can be used for pointing out where C Git is installed. Modifying PATH is the recommended option if C Git is installed.

  • We try to use the same notation of $HOME as C Git does. On Windows this is often not the same value as the user.home system property.

Features

  • org.eclipse.jgit

    • Read loose and packed commits, trees, blobs, including deltafied objects.

    • Read objects from shared repositories

    • Write loose commits, trees, blobs.

    • Write blobs from local files or Java InputStreams.

    • Read blobs as Java InputStreams.

    • Copy trees to local directory, or local directory to a tree.

    • Lazily loads objects as necessary.

    • Read and write .git/config files.

    • Create a new repository.

    • Read and write refs, including walking through symrefs.

    • Read, update and write the Git index.

    • Checkout in dirty working directory if trivial.

    • Walk the history from a given set of commits looking for commits introducing changes in files under a specified path.

    • Object transport

      Fetch via ssh, git, http, Amazon S3 and bundles. Push via ssh, git and Amazon S3. JGit does not yet deltify the pushed packs so they may be a lot larger than C Git packs.

    • Garbage collection

    • Merge

    • Rebase

    • And much more

  • org.eclipse.jgit.pgm

    • Assorted set of command line utilities. Mostly for ad-hoc testing of jgit log, glog, fetch etc.
  • org.eclipse.jgit.ant

    • Ant tasks
  • org.eclipse.jgit.archive

    • Support for Zip/Tar and other formats
  • org.eclipse.http

    • HTTP client and server support

Missing Features

There are some missing features:

  • verifying signed commits
  • signing tags
  • signing push

Support

Post questions, comments or discussions to the jgit-dev@eclipse.org mailing list. You need to be subscribed to post. File bugs and enhancement requests in Bugzilla.

Contributing

See the EGit Contributor Guide.

About Git

More information about Git, its repository format, and the canonical C based implementation can be obtained from the Git website.