Fix dirt calculation across restarts

Author: lucaong

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:

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
 

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)