[PATCH] config: set pack.useSparse=true by default

From: Derrick Stolee via GitGitGadget <gitgitgadget@gmail.com>
Date: Mar 19, 2020, 01:58 UTC
Message-ID: <pull.585.git.1584583110914.gitgitgadget@gmail.com>

From: Derrick Stolee <dstolee@microsoft.com>

The pack.useSparse config option was introduced by 3d036eb0 (pack-objects: create pack.useSparse setting, 2019-01-19) and was first available in v2.21.0. When enabled, the pack-objects process during 'git push' will use a sparse tree walk when deciding which trees and blobs to send to the remote. The algorithm was introduced by d5d2e93 (revision: implement sparse algorithm, 2019-01-16) and has been in production use by VFS for Git since around that time. The features.experimental config option also enabled pack.useSparse, so hopefully that has also increased exposure.

It is worth noting that pack.useSparse has a possibility of sending more objects across a push, but requires a special arrangement of exact _copies_ across directories. There is a test in t5322-pack-objects-sparse.sh that demonstrates this possibility.

Since the downside is unlikely but the upside is significant, set the default value of pack.useSparse to true. Remove it from the set of options implied by features.experimental.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
    config: set pack.useSparse=true by default
    
    Here is a small patch to convert pack.useSparse to true by default. It's
    been released for over a year, so the feature is quite stable. I'm
    submitting this now to allow it to cook for a while during the next
    release cycle.
    
    Thanks, -Stolee

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-585%2Fderrickstolee%2Fpack-use-sparse-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-585/derrickstolee/pack-use-sparse-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/585

 Documentation/config/feature.txt | 3 ---
 Documentation/config/pack.txt    | 4 ++--
 repo-settings.c                  | 3 ++-
 3 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/Documentation/config/feature.txt b/Documentation/config/feature.txt
index 875f8c8a66f..4e3a5c0cebc 100644
--- a/Documentation/config/feature.txt
+++ b/Documentation/config/feature.txt
@@ -12,9 +12,6 @@ feature.experimental::
 	setting if you are interested in providing feedback on experimental
 	features. The new default values are:
 +
-* `pack.useSparse=true` uses a new algorithm when constructing a pack-file
-which can improve `git push` performance in repos with many files.
-+
 * `fetch.negotiationAlgorithm=skipping` may improve fetch negotiation times by
 skipping more commits at a time, reducing the number of round trips.
 +
diff --git a/Documentation/config/pack.txt b/Documentation/config/pack.txt
index 0dac5805816..837f1b16792 100644
--- a/Documentation/config/pack.txt
+++ b/Documentation/config/pack.txt
@@ -119,8 +119,8 @@ pack.useSparse::
 	objects. This can have significant performance benefits when
 	computing a pack to send a small change. However, it is possible
 	that extra objects are added to the pack-file if the included
-	commits contain certain types of direct renames. Default is `false`
-	unless `feature.experimental` is enabled.
+	commits contain certain types of direct renames. Default is
+	`true`.
 
 pack.writeBitmaps (deprecated)::
 	This is a deprecated synonym for `repack.writeBitmaps`.
diff --git a/repo-settings.c b/repo-settings.c
index a703e407a3f..dc6817daa95 100644
--- a/repo-settings.c
+++ b/repo-settings.c
@@ -45,6 +45,8 @@ void prepare_repo_settings(struct repository *r)
 
 	if (!repo_config_get_bool(r, "pack.usesparse", &value))
 		r->settings.pack_use_sparse = value;
+	UPDATE_DEFAULT_BOOL(r->settings.pack_use_sparse, 1);
+
 	if (!repo_config_get_bool(r, "feature.manyfiles", &value) && value) {
 		UPDATE_DEFAULT_BOOL(r->settings.index_version, 4);
 		UPDATE_DEFAULT_BOOL(r->settings.core_untracked_cache, UNTRACKED_CACHE_WRITE);
@@ -52,7 +54,6 @@ void prepare_repo_settings(struct repository *r)
 	if (!repo_config_get_bool(r, "fetch.writecommitgraph", &value))
 		r->settings.fetch_write_commit_graph = value;
 	if (!repo_config_get_bool(r, "feature.experimental", &value) && value) {
-		UPDATE_DEFAULT_BOOL(r->settings.pack_use_sparse, 1);
 		UPDATE_DEFAULT_BOOL(r->settings.fetch_negotiation_algorithm, FETCH_NEGOTIATION_SKIPPING);
 		UPDATE_DEFAULT_BOOL(r->settings.fetch_write_commit_graph, 1);
 	}

base-commit: 6c85aac65fb455af85745130ce35ddae4678db84

-- 
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