From 79b4062f1b19416d21d528da547a09851c48317c Mon Sep 17 00:00:00 2001
From: Luca Ongaro <mail@lucaongaro.eu>
Date: Wed, 2 Oct 2024 15:36:10 +0200
Subject: [PATCH] Fix dirt calculation across restarts

---
 CHANGELOG.md        |  4 ++++
 lib/cubdb/btree.ex  |  2 +-
 test/cubdb_test.exs | 18 ++++++++++++++++++
 3 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index bdd556f..f41c076 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,10 @@ reports changes here.
 
   - Add function `CubDB.writes_since_compaction/1` to get the number of writes since the last successful compaction
 
+Bug fixes:
+
+  - Fix dirt calculation upon restart of `CubDB`
+
 ## v2.0.2 (2023-01-01)
 
 Bug fixes:
diff --git a/lib/cubdb/btree.ex b/lib/cubdb/btree.ex
index b02f4c7..403e943 100644
--- a/lib/cubdb/btree.ex
+++ b/lib/cubdb/btree.ex
@@ -244,7 +244,7 @@ defmodule CubDB.Btree do
   # updates won't be committed to the database and will be lost in case of a
   # restart.
   def commit(tree = %Btree{store: store, size: size, root_loc: root_loc, dirt: dirt}) do
-    Store.put_header(store, header(size: size, location: root_loc, dirt: dirt + 1))
+    Store.put_header(store, header(size: size, location: root_loc, dirt: dirt))
     tree
   end
 
diff --git a/test/cubdb_test.exs b/test/cubdb_test.exs
index 160087d..64b2143 100644
--- a/test/cubdb_test.exs
+++ b/test/cubdb_test.exs
@@ -1003,6 +1003,24 @@ defmodule CubDBTest do
     refute_received :compaction_started
   end
 
+  test "dirt calculation is consistent after restart", %{tmp_dir: tmp_dir} do
+    {:ok, db} = CubDB.start_link(data_dir: tmp_dir, auto_compact: false)
+
+    CubDB.put(db, "foo", 123)
+    CubDB.put(db, "bar", 234)
+    CubDB.delete(db, "foo")
+    CubDB.clear(db)
+
+    original_dirt_factor = CubDB.dirt_factor(db)
+    original_writes_since_compaction = CubDB.dirt_factor(db)
+
+    CubDB.stop(db)
+
+    {:ok, db} = CubDB.start_link(data_dir: tmp_dir, auto_compact: false)
+    assert original_dirt_factor == CubDB.dirt_factor(db)
+    assert original_writes_since_compaction == CubDB.dirt_factor(db)
+  end
+
   test "auto compaction is active by default", %{tmp_dir: tmp_dir} do
     {:ok, db} = CubDB.start_link(tmp_dir)