glossary: add reachability bitmap description

Describe the purpose of the reachability bitmap.

Signed-off-by: Philip Oakley <philipoakley@iee.email>
Signed-off-by: Taylor Blau <me@ttaylorr.com>

diff --git a/Documentation/glossary-content.txt b/Documentation/glossary-content.txt
index a5267102788b40cae10d1aa25b689269eb49d682..5a537268e275e45142640820942004b5cd731dbb 100644 (file)
--- a/Documentation/glossary-content.txt
+++ b/Documentation/glossary-content.txt
@@ -508,6 +508,14 @@ exclude;;
        <<def_tree_object,trees>> to the trees or <<def_blob_object,blobs>>
        that they contain.
 
+[[def_reachability_bitmap]]reachability bitmaps::
+       Reachability bitmaps store information about the
+       <<def_reachable,reachability>> of a selected set of commits in
+       a packfile, or a multi-pack index (MIDX), to speed up object search.
+       The bitmaps are stored in a ".bitmap" file. A repository may have at
+       most one bitmap file in use. The bitmap file may belong to either one
+       pack, or the repository's multi-pack index (if it exists).
+
 [[def_rebase]]rebase::
        To reapply a series of changes from a <<def_branch,branch>> to a
        different base, and reset the <<def_head,head>> of that branch