From 3f267a112820f3bdf6b82362680ea6339f0e5f86 Mon Sep 17 00:00:00 2001 From: Taylor Blau Date: Wed, 31 Mar 2021 21:32:14 -0400 Subject: builtin/pack-objects.c: respect 'pack.preferBitmapTips' When writing a new pack with a bitmap, it is sometimes convenient to indicate some reference prefixes which should receive priority when selecting which commits to receive bitmaps. A truly motivated caller could accomplish this by setting 'pack.islandCore', (since all commits in the core island are similarly marked as preferred) but this requires callers to opt into using delta islands, which they may or may not want to do. Introduce a new multi-valued configuration, 'pack.preferBitmapTips' to allow callers to specify a list of reference prefixes. All references which have a prefix contained in 'pack.preferBitmapTips' will mark their tips as "preferred" in the same way as commits are marked as preferred for selection by 'pack.islandCore'. The choice of the verb "prefer" is intentional: marking the NEEDS_BITMAP flag on an object does *not* guarantee that that object will receive a bitmap. It merely guarantees that that commit will receive a bitmap over any *other* commit in the same window by bitmap_writer_select_commits(). The test this patch adds reflects this quirk, too. It only tests that a commit (which didn't receive bitmaps by default) is selected for bitmaps after changing the value of 'pack.preferBitmapTips' to include it. Other commits may lose their bitmaps as a byproduct of how the selection process works (bitmap_writer_select_commits() ignores the remainder of a window after seeing a commit with the NEEDS_BITMAP flag). This configuration will aide in selecting important references for multi-pack bitmaps, since they do not respect the same pack.islandCore configuration. (They could, but doing so may be confusing, since it is packs--not bitmaps--which are influenced by the delta-islands configuration). In a fork network repository (one which lists all forks of a given repository as remotes), for example, it is useful to set pack.preferBitmapTips to 'refs/remotes//heads' and 'refs/remotes//tags', where '' is an opaque identifier referring to the repository which is at the base of the fork chain. Suggested-by: Jeff King Signed-off-by: Taylor Blau Signed-off-by: Junio C Hamano --- Documentation/config/pack.txt | 15 +++++++++++++++ 1 file changed, 15 insertions(+) (limited to 'Documentation/config') diff --git a/Documentation/config/pack.txt b/Documentation/config/pack.txt index 3da4ea98e2..c0844d8d8e 100644 --- a/Documentation/config/pack.txt +++ b/Documentation/config/pack.txt @@ -122,6 +122,21 @@ pack.useSparse:: commits contain certain types of direct renames. Default is `true`. +pack.preferBitmapTips:: + When selecting which commits will receive bitmaps, prefer a + commit at the tip of any reference that is a suffix of any value + of this configuration over any other commits in the "selection + window". ++ +Note that setting this configuration to `refs/foo` does not mean that +the commits at the tips of `refs/foo/bar` and `refs/foo/baz` will +necessarily be selected. This is because commits are selected for +bitmaps from within a series of windows of variable length. ++ +If a commit at the tip of any reference which is a suffix of any value +of this configuration is seen in a window, it is immediately given +preference over any other commit in that window. + pack.writeBitmaps (deprecated):: This is a deprecated synonym for `repack.writeBitmaps`. -- cgit v1.2.3