From: Christian Couder <christian.couder@gmail.com>
To: git@vger.kernel.org
Cc: Junio C Hamano <gitster@pobox.com>, Jeff King <peff@peff.net>,
Ben Peart <Ben.Peart@microsoft.com>,
Jonathan Tan <jonathantanmy@google.com>,
Jonathan Nieder <jrnieder@gmail.com>,
Nguyen Thai Ngoc Duy <pclouds@gmail.com>,
Mike Hommey <mh@glandium.org>,
Lars Schneider <larsxschneider@gmail.com>,
Eric Wong <e@80x24.org>,
Christian Couder <chriscool@tuxfamily.org>,
Jeff Hostetler <jeffhost@microsoft.com>,
Eric Sunshine <sunshine@sunshineco.com>,
Beat Bolli <dev+git@drbeat.li>
Subject: [PATCH v4 10/11] partial-clone: add multiple remotes in the doc
Date: Mon, 1 Apr 2019 18:40:44 +0200 [thread overview]
Message-ID: <20190401164045.17328-11-chriscool@tuxfamily.org> (raw)
In-Reply-To: <20190401164045.17328-1-chriscool@tuxfamily.org>
While at it, let's remove a reference to ODB effort as the ODB
effort has been replaced by directly enhancing partial clone
and promisor remote features.
Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
---
Documentation/technical/partial-clone.txt | 83 ++++++++++++++++-------
1 file changed, 58 insertions(+), 25 deletions(-)
diff --git a/Documentation/technical/partial-clone.txt b/Documentation/technical/partial-clone.txt
index 896c7b3878..58adcc5ce1 100644
--- a/Documentation/technical/partial-clone.txt
+++ b/Documentation/technical/partial-clone.txt
@@ -100,18 +100,18 @@ or commits that reference missing trees.
Handling Missing Objects
------------------------
-- An object may be missing due to a partial clone or fetch, or missing due
- to repository corruption. To differentiate these cases, the local
- repository specially indicates such filtered packfiles obtained from the
- promisor remote as "promisor packfiles".
+- An object may be missing due to a partial clone or fetch, or missing
+ due to repository corruption. To differentiate these cases, the
+ local repository specially indicates such filtered packfiles
+ obtained from promisor remotes as "promisor packfiles".
+
These promisor packfiles consist of a "<name>.promisor" file with
arbitrary contents (like the "<name>.keep" files), in addition to
their "<name>.pack" and "<name>.idx" files.
- The local repository considers a "promisor object" to be an object that
- it knows (to the best of its ability) that the promisor remote has promised
- that it has, either because the local repository has that object in one of
+ it knows (to the best of its ability) that promisor remotes have promised
+ that they have, either because the local repository has that object in one of
its promisor packfiles, or because another promisor object refers to it.
+
When Git encounters a missing object, Git can see if it is a promisor object
@@ -123,7 +123,7 @@ expensive-to-modify list of missing objects.[a]
- Since almost all Git code currently expects any referenced object to be
present locally and because we do not want to force every command to do
a dry-run first, a fallback mechanism is added to allow Git to attempt
- to dynamically fetch missing objects from the promisor remote.
+ to dynamically fetch missing objects from promisor remotes.
+
When the normal object lookup fails to find an object, Git invokes
fetch-object to try to get the object from the server and then retry
@@ -157,8 +157,7 @@ and prefetch those objects in bulk.
+
We are not happy with this global variable and would like to remove it,
but that requires significant refactoring of the object code to pass an
-additional flag. We hope that concurrent efforts to add an ODB API can
-encompass this.
+additional flag.
Fetching Missing Objects
@@ -182,21 +181,53 @@ has been updated to not use any object flags when the corresponding argument
though they are not necessary.
+Using many promisor remotes
+---------------------------
+
+Many promisor remotes can be configured and used.
+
+This allows for example a user to have multiple geographically-close
+cache servers for fetching missing blobs while continuing to do
+filtered `git-fetch` commands from the central server.
+
+When fetching objects, promisor remotes are tried one after the other
+until all the objects have been fetched.
+
+Remotes that are considered "promisor" remotes are those specified by
+the following configuration variables:
+
+- `extensions.partialClone = <name>`
+
+- `remote.<name>.promisor = true`
+
+- `remote.<name>.partialCloneFilter = ...`
+
+Only one promisor remote can be configured using the
+`extensions.partialClone` config variable. This promisor remote will
+be the last one tried when fetching objects.
+
+The other promisor remotes will be tried in the order they appear in
+the config file.
+
Current Limitations
-------------------
-- The remote used for a partial clone (or the first partial fetch
- following a regular clone) is marked as the "promisor remote".
+- It is not possible to specify the order in which the promisor
+ remotes are tried in other ways than the order in which they appear
+ in the config file.
+
-We are currently limited to a single promisor remote and only that
-remote may be used for subsequent partial fetches.
+It is also not possible to specify an order to be used when fetching
+from one remote and a different order when fetching from another
+remote.
+
+- It is not possible to push only specific objects to a promisor
+ remote.
+
-We accept this limitation because we believe initial users of this
-feature will be using it on repositories with a strong single central
-server.
+It is not possible to push at the same time to multiple promisor
+remote in a specific order.
-- Dynamic object fetching will only ask the promisor remote for missing
- objects. We assume that the promisor remote has a complete view of the
+- Dynamic object fetching will only ask promisor remotes for missing
+ objects. We assume that promisor remotes have a complete view of the
repository and can satisfy all such requests.
- Repack essentially treats promisor and non-promisor packfiles as 2
@@ -218,15 +249,17 @@ server.
Future Work
-----------
-- Allow more than one promisor remote and define a strategy for fetching
- missing objects from specific promisor remotes or of iterating over the
- set of promisor remotes until a missing object is found.
+- Improve the way to specify the order in which promisor remotes are
+ tried.
+
-A user might want to have multiple geographically-close cache servers
-for fetching missing blobs while continuing to do filtered `git-fetch`
-commands from the central server, for example.
+For example this could allow to specify explicitly something like:
+"When fetching from this remote, I want to use these promisor remotes
+in this order, though, when pushing or fetching to that remote, I want
+to use those promisor remotes in that order."
+
+- Allow pushing to promisor remotes.
+
-Or the user might want to work in a triangular work flow with multiple
+The user might want to work in a triangular work flow with multiple
promisor remotes that each have an incomplete view of the repository.
- Allow repack to work on promisor packfiles (while keeping them distinct
--
2.21.0.203.gd44fa53258
next prev parent reply other threads:[~2019-04-01 16:41 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-01 16:40 [PATCH v4 00/11] Many promisor remotes Christian Couder
2019-04-01 16:40 ` [PATCH v4 01/11] fetch-object: make functions return an error code Christian Couder
2019-04-01 16:40 ` [PATCH v4 02/11] Add initial support for many promisor remotes Christian Couder
2019-04-03 22:08 ` SZEDER Gábor
2019-04-04 8:02 ` Christian Couder
2019-04-01 16:40 ` [PATCH v4 03/11] promisor-remote: implement promisor_remote_get_direct() Christian Couder
2019-04-01 16:40 ` [PATCH v4 04/11] promisor-remote: add promisor_remote_reinit() Christian Couder
2019-04-01 16:40 ` [PATCH v4 05/11] promisor-remote: use repository_format_partial_clone Christian Couder
2019-04-01 16:40 ` [PATCH v4 06/11] Use promisor_remote_get_direct() and has_promisor_remote() Christian Couder
2019-04-01 16:40 ` [PATCH v4 07/11] promisor-remote: parse remote.*.partialclonefilter Christian Couder
2019-04-01 16:40 ` [PATCH v4 08/11] builtin/fetch: remove unique promisor remote limitation Christian Couder
2019-04-01 16:40 ` [PATCH v4 09/11] t0410: test fetching from many promisor remotes Christian Couder
2019-04-05 0:56 ` SZEDER Gábor
2019-04-01 16:40 ` Christian Couder [this message]
2019-04-01 16:40 ` [PATCH v4 11/11] remote: add promisor and partial clone config to the doc Christian Couder
2019-04-04 7:23 ` [PATCH v4 00/11] Many promisor remotes Junio C Hamano
2019-04-04 7:59 ` Christian Couder
2019-04-05 20:07 ` Johannes Schindelin
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