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authorLibravatar Jonathan Tan <jonathantanmy@google.com>2021-08-16 14:09:51 -0700
committerLibravatar Junio C Hamano <gitster@pobox.com>2021-09-08 11:47:36 -0700
commita35e03dee0e8daa442227018ecd180ae1c1b39bc (patch)
tree858b7c974141a62c73222b6e758837a202738681 /t
parentGit 2.33-rc1 (diff)
downloadtgif-a35e03dee0e8daa442227018ecd180ae1c1b39bc.tar.xz
submodule: lazily add submodule ODBs as alternates
Teach Git to add submodule ODBs as alternates to the object store of the_repository only upon the first access of an object not in the_repository, and not when add_submodule_odb() is called. This provides a means of gradually migrating from accessing a submodule's object through alternates to accessing a submodule's object by explicitly passing its repository object. Any Git command can declare that it might access submodule objects by calling add_submodule_odb() (as they do now), but the submodule ODBs themselves will not be added until needed, so individual commands and/or combinations of arguments can be migrated one by one. [The advantage of explicit repository-object passing is code clarity (it is clear which repository an object read is from), performance (there is no need to linearly search through all submodule ODBs whenever an object is accessed from any repository, whether superproject or submodule), and the possibility of future features like partial clone submodules (which right now is not possible because if an object is missing, we do not know which repository to lazy-fetch into).] This commit also introduces an environment variable that a test may set to make the actual registration of alternates fatal, in order to demonstrate that its codepaths do not need this registration. Signed-off-by: Jonathan Tan <jonathantanmy@google.com> Reviewed-by: Emily Shaffer <emilyshaffer@google.com> Reviewed-by: Matheus Tavares <matheus.bernardino@usp.br> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Diffstat (limited to 't')
-rw-r--r--t/README10
1 files changed, 10 insertions, 0 deletions
diff --git a/t/README b/t/README
index 9e70122302..8b67b4f00b 100644
--- a/t/README
+++ b/t/README
@@ -448,6 +448,16 @@ GIT_TEST_CHECKOUT_WORKERS=<n> overrides the 'checkout.workers' setting
to <n> and 'checkout.thresholdForParallelism' to 0, forcing the
execution of the parallel-checkout code.
+GIT_TEST_FATAL_REGISTER_SUBMODULE_ODB=<boolean>, when true, makes
+registering submodule ODBs as alternates a fatal action. Support for
+this environment variable can be removed once the migration to
+explicitly providing repositories when accessing submodule objects is
+complete (in which case we might want to replace this with a trace2
+call so that users can make it visible if accessing submodule objects
+without an explicit repository still happens) or needs to be abandoned
+for whatever reason (in which case the migrated codepaths still retain
+their performance benefits).
+
Naming Tests
------------