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[128.78.31.246]) by smtp.gmail.com with ESMTPSA id k86sm11577890wmi.16.2017.06.20.00.55.47 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Tue, 20 Jun 2017 00:55:48 -0700 (PDT) From: Christian Couder X-Google-Original-From: Christian Couder To: git@vger.kernel.org Cc: Junio C Hamano , Jeff King , Ben Peart , Nguyen Thai Ngoc Duy , Mike Hommey , Lars Schneider , Eric Wong , Christian Couder Subject: [RFC/PATCH v4 00/49] Add initial experimental external ODB support Date: Tue, 20 Jun 2017 09:54:34 +0200 Message-Id: <20170620075523.26961-1-chriscool@tuxfamily.org> X-Mailer: git-send-email 2.13.1.565.gbfcd7a9048 Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org Goal ~~~~ Git can store its objects only in the form of loose objects in separate files or packed objects in a pack file. To be able to better handle some kind of objects, for example big blobs, it would be nice if Git could store its objects in other object databases (ODB). To do that, this patch series makes it possible to register commands, also called "helpers", using "odb..command" config variables, to access external ODBs where objects can be stored and retrieved. External ODBs should be able to tranfer information about the blobs they store. This patch series shows how this is possible using kind of replace refs. Design ~~~~~~ * The "helpers" (registered commands) Each helper manages access to one external ODB. There are now 2 different modes for helper: - When "odb..scriptMode" is set to "true", the helper is launched each time Git wants to communicate with the external ODB. - When "odb..scriptMode" is not set or set to "false", then the helper is launched once as a sub-process (using sub-process.h), and Git communicates with it using packet lines. A helper can be given different instructions by Git. The instructions that are supported are negociated at the beginning of the communication using a capability mechanism. For now the following instructions are supported: - "have": the helper should respond with the sha1, size and type of all the objects the external ODB contains, one object per line. - "get ": the helper should then read from the external ODB the content of the object corresponding to and pass it to Git. - "put ": the helper should then read from from Git an object and store it in the external ODB. Currently "have" and "put" are optional. There are 3 different kinds of "get" instructions depending on how the helper passes objects to Git: - "fault_in": the helper will write the requested objects directly into the regular Git object database, and then Git will retry reading it from there. - "git_object": the helper will send the object as a Git object. - "plain_object": the helper will send the object (a blob) as a raw object. (The blob content will be sent as is.) For now the kind of "get" that is supported is read from the "odb..fetchKind" configuration variable, but in the future it should be decided as part of the capability negociation. * Transfering information To tranfer information about the blobs stored in external ODB, some special refs, called "odb ref", similar as replace refs, are used in the tests of this series, but in general nothing forces the helper to use that mechanism. The external odb helper is responsible for using and creating the refs in refs/odbs//, if it wants to do that. It is free for example to just create one ref, as it is also free to create many refs. Git would just transmit the refs that have been created by this helper, if Git is asked to do so. For now in the tests there is one odb ref per blob, as it is simple and as it is similar to what git-lfs does. Each ref name is refs/odbs// where is the sha1 of the blob stored in the external odb named . These odb refs point to a blob that is stored in the Git repository and contain information about the blob stored in the external odb. This information can be specific to the external odb. The repos can then share this information using commands like: `git fetch origin "refs/odbs//*:refs/odbs//*"` At the end of the current patch series, "git clone" is teached a "--initial-refspec" option, that asks it to first fetch some specified refs. This is used in the tests to fetch the odb refs first. This way only one "git clone" command can setup a repo using the external ODB mechanism as long as the right helper is installed on the machine and as long as the following options are used: - "--initial-refspec " to fetch the odb refspec - "-c odb..command=" to configure the helper There is also a test script that shows that the "--initial-refspec" option along with the external ODB mechanism can be used to implement cloning using bundles. * External object database This RFC patch series shows in the tests: - how to use another git repository as an external ODB (storing Git objects) - how to use an http server as an external ODB (storing plain objects) (This works in both script mode and sub-process mode.) * Performance So the sub-process mode, which is now the default, has been implemented in this new version of this patch series. This has been implemented using the refactoring that Ben Peart did on top of Lars Schneider's work on using sub-processes and packet lines in the smudge/clean filters for git-lfs. This also uses further work from Ben Peart called "read object process". See: http://public-inbox.org/git/20170113155253.1644-1-benpeart@microsoft.com/ http://public-inbox.org/git/20170322165220.5660-1-benpeart@microsoft.com/ Thanks to this, the external ODB mechanism should in the end perform as well as the git-lfs mechanism when many objects should be transfered. Implementation ~~~~~~~~~~~~~~ * Mechanism to call the registered commands This series adds a set of function in external-odb.{c,h} that are called by the rest of Git to manage all the external ODBs. These functions use 'struct odb_helper' and its associated functions defined in odb-helper.{c,h} to talk to the different external ODBs by launching the configured "odb..command" commands and writing to or reading from them. * ODB refs For now odb ref management is only implemented in a helper in t0410. When a new blob is added to an external odb, its sha1, size and type are writen in another new blob and the odb ref is created. When the list of existing blobs is requested from the external odb, the content of the blobs pointed to by the odb refs can also be used by the odb to claim that it can get the objects. When a blob is actually requested from the external odb, it can use the content stored in the blobs pointed to by the odb refs to get the actual blobs and then pass them. Highlevel view of the patches in the series ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ - Patch 1/49 is a small code cleanup that I already sent to the mailing list but will probably be removed in the end bdue to ongoing work on "git clone" - Patches 02/49 to 08/49 create a Git/Packet.pm module by refactoring "t0021/rot13-filter.pl". Functions from this new module will be used later in test scripts. - Patches 09/49 to 16/49 create the external ODB insfrastructure in external-odb.{c,h} and odb-helper.{c,h} for the script mode. - Patches 17/49 to 23/49 improve lib-http to make it possible to use it as an external ODB to test storing blobs in an HTTP server. - Patches 24/49 to 44/49 improve the external ODB insfrastructure to support sub-processes and make everything work using them. - Patches 45/49 to 49/49 add the --initial-refspec to git clone along with tests. Future work ~~~~~~~~~~~ First sorry about the state of this patch series, it is not as clean as I would have liked, butI think it is interesting to get feedback from the mailing list at this point, because the previous RFC was sent a long time ago and a lot of things changed. So a big part of the future work will be about cleaning this patch series. Other things I think I am going to do: - Previous work and discussions ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ (Sorry for the old Gmane links, I will try to replace them with public-inbox.org at one point.) Peff started to work on this and discuss this some years ago: http://thread.gmane.org/gmane.comp.version-control.git/206886/focus=207040 http://thread.gmane.org/gmane.comp.version-control.git/247171 http://thread.gmane.org/gmane.comp.version-control.git/202902/focus=203020 His work, which is not compile-tested any more, is still there: https://github.com/peff/git/commits/jk/external-odb-wip Initial discussions about this new series are there: http://thread.gmane.org/gmane.comp.version-control.git/288151/focus=295160 Version 1, 2 and 3 of this RFC/PATCH series are here: https://public-inbox.org/git/20160613085546.11784-1-chriscool@tuxfamily.org/ https://public-inbox.org/git/20160628181933.24620-1-chriscool@tuxfamily.org/ https://public-inbox.org/git/20161130210420.15982-1-chriscool@tuxfamily.org/ Some of the discussions related to Ben Peart's work that is used by this series are here: http://public-inbox.org/git/20170113155253.1644-1-benpeart@microsoft.com/ http://public-inbox.org/git/20170322165220.5660-1-benpeart@microsoft.com/ Links ~~~~~ This patch series is available here: https://github.com/chriscool/git/commits/external-odb Version 1, 2 and 3 are here: https://github.com/chriscool/git/commits/gl-external-odb12 https://github.com/chriscool/git/commits/gl-external-odb22 https://github.com/chriscool/git/commits/gl-external-odb61 Ben Peart (4): Documentation: add read-object-protocol.txt contrib: add long-running-read-object/example.pl Add t0410 to test read object mechanism odb-helper: add read_object_process() Christian Couder (43): builtin/clone: get rid of 'value' strbuf t0021/rot13-filter: refactor packet reading functions t0021/rot13-filter: improve 'if .. elsif .. else' style Add Git/Packet.pm from parts of t0021/rot13-filter.pl t0021/rot13-filter: use Git/Packet.pm Git/Packet.pm: improve error message Git/Packet.pm: add packet_initialize() Git/Packet: add capability functions t0400: add 'put' command to odb-helper script external odb: add write support external-odb: accept only blobs for now t0400: add test for external odb write support Add GIT_NO_EXTERNAL_ODB env variable Add t0410 to test external ODB transfer lib-httpd: pass config file to start_httpd() lib-httpd: add upload.sh lib-httpd: add list.sh lib-httpd: add apache-e-odb.conf odb-helper: add 'store_plain_objects' to 'struct odb_helper' pack-objects: don't pack objects in external odbs t0420: add test with HTTP external odb odb-helper: start fault in implementation external-odb: add external_odb_fault_in_object() odb-helper: add script_mode external-odb: add external_odb_get_capabilities() t04*: add 'get_cap' support to helpers odb-helper: call odb_helper_lookup() with 'have' capability odb-helper: fix odb_helper_fetch_object() for read_object Add t0460 to test passing git objects odb-helper: add read_packetized_git_object_to_fd() odb-helper: add read_packetized_plain_object_to_fd() Add t0470 to test passing plain objects odb-helper: add write_object_process() Add t0480 to test "have" capability and plain objects external-odb: add external_odb_do_fetch_object() odb-helper: advertise 'have' capability odb-helper: advertise 'put' capability odb-helper: add have_object_process() clone: add initial param to write_remote_refs() clone: add --initial-refspec option clone: disable external odb before initial clone Add test for 'clone --initial-refspec' t: add t0430 to test cloning using bundles Jeff King (2): Add initial external odb support external odb foreach Documentation/technical/read-object-protocol.txt | 102 +++ Makefile | 2 + builtin/clone.c | 91 ++- builtin/pack-objects.c | 4 + cache.h | 18 + contrib/long-running-read-object/example.pl | 114 +++ environment.c | 4 + external-odb.c | 220 +++++ external-odb.h | 17 + odb-helper.c | 987 +++++++++++++++++++++++ odb-helper.h | 47 ++ perl/Git/Packet.pm | 118 +++ sha1_file.c | 117 ++- t/lib-httpd.sh | 8 +- t/lib-httpd/apache-e-odb.conf | 214 +++++ t/lib-httpd/list.sh | 41 + t/lib-httpd/upload.sh | 45 ++ t/t0021/rot13-filter.pl | 97 +-- t/t0400-external-odb.sh | 85 ++ t/t0410-transfer-e-odb.sh | 148 ++++ t/t0420-transfer-http-e-odb.sh | 159 ++++ t/t0430-clone-bundle-e-odb.sh | 91 +++ t/t0450-read-object.sh | 30 + t/t0450/read-object | 56 ++ t/t0460-read-object-git.sh | 29 + t/t0460/read-object-git | 67 ++ t/t0470-read-object-http-e-odb.sh | 123 +++ t/t0470/read-object-plain | 93 +++ t/t0480-read-object-have-http-e-odb.sh | 123 +++ t/t0480/read-object-plain-have | 116 +++ t/t5616-clone-initial-refspec.sh | 48 ++ 31 files changed, 3296 insertions(+), 118 deletions(-) create mode 100644 Documentation/technical/read-object-protocol.txt create mode 100644 contrib/long-running-read-object/example.pl create mode 100644 external-odb.c create mode 100644 external-odb.h create mode 100644 odb-helper.c create mode 100644 odb-helper.h create mode 100644 perl/Git/Packet.pm create mode 100644 t/lib-httpd/apache-e-odb.conf create mode 100644 t/lib-httpd/list.sh create mode 100644 t/lib-httpd/upload.sh create mode 100755 t/t0400-external-odb.sh create mode 100755 t/t0410-transfer-e-odb.sh create mode 100755 t/t0420-transfer-http-e-odb.sh create mode 100755 t/t0430-clone-bundle-e-odb.sh create mode 100755 t/t0450-read-object.sh create mode 100755 t/t0450/read-object create mode 100755 t/t0460-read-object-git.sh create mode 100755 t/t0460/read-object-git create mode 100755 t/t0470-read-object-http-e-odb.sh create mode 100755 t/t0470/read-object-plain create mode 100755 t/t0480-read-object-have-http-e-odb.sh create mode 100755 t/t0480/read-object-plain-have create mode 100755 t/t5616-clone-initial-refspec.sh -- 2.13.1.565.gbfcd7a9048