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-rw-r--r--Documentation/technical/commit-graph.txt15
1 files changed, 15 insertions, 0 deletions
diff --git a/Documentation/technical/commit-graph.txt b/Documentation/technical/commit-graph.txt
index 473032e476..aed4350a59 100644
--- a/Documentation/technical/commit-graph.txt
+++ b/Documentation/technical/commit-graph.txt
@@ -266,6 +266,21 @@ The merge strategy values (2 for the size multiple, 64,000 for the maximum
number of commits) could be extracted into config settings for full
flexibility.
+## Deleting graph-{hash} files
+
+After a new tip file is written, some `graph-{hash}` files may no longer
+be part of a chain. It is important to remove these files from disk, eventually.
+The main reason to delay removal is that another process could read the
+`commit-graph-chain` file before it is rewritten, but then look for the
+`graph-{hash}` files after they are deleted.
+
+To allow holding old split commit-graphs for a while after they are unreferenced,
+we update the modified times of the files when they become unreferenced. Then,
+we scan the `$OBJDIR/info/commit-graphs/` directory for `graph-{hash}`
+files whose modified times are older than a given expiry window. This window
+defaults to zero, but can be changed using command-line arguments or a config
+setting.
+
## Chains across multiple object directories
In a repo with alternates, we look for the `commit-graph-chain` file starting