diff --git a/lib/daybreak/db.rb b/lib/daybreak/db.rb
index dae504c..645b003 100644
--- a/lib/daybreak/db.rb
+++ b/lib/daybreak/db.rb
@@ -244,8 +244,9 @@ def clear
 
     # Compact the database to remove stale commits and reduce the file size.
     # @return [DB] self
-    def compact
+    def compact(options = {})
       sync
+      return self unless compact_needed?(options)
       with_tmpfile do |path, file|
         # Compactified database has the same size -> return
         return self if @pos == file.write(dump)
@@ -282,7 +283,15 @@ def closed?
 
     private
 
-    # The block used in @table for new entries
+    def compact_needed?(options)
+      return true if options[:force]
+      options[:ratio] ||= 2 # Two log records per table record
+      options[:reduction] ||= 4096 # One filesystem block, otherwise we won't gain
+      logsize > options[:ratio] * size || # Log size vs table size ratio
+        bytesize - (bytesize * size / logsize) > options[:reduction] # Estimate log size reduction
+    end
+
+    # The block used in @table for new records
     def hash_default(_, key)
       if @default != nil
         value = @default.respond_to?(:call) ? @default.call(key) : @default
diff --git a/test/test.rb b/test/test.rb
index adb1003..ee5b558 100644
--- a/test/test.rb
+++ b/test/test.rb
@@ -64,7 +64,7 @@
   it 'should persist after compact' do
     @db['1'] = 'xy'
     @db['1'] = 'z'
-    assert_equal @db.compact, @db
+    assert_equal @db.compact(:force => true), @db
     @db['1'] = '4'
     @db['4'] = '1'
     assert_equal @db.close, nil
@@ -79,7 +79,7 @@
 
     @db['1'] = 'xy'
     @db['1'] = 'z'
-    assert_equal @db.compact, @db
+    assert_equal @db.compact(:force => true), @db
     @db['1'] = '4'
     @db['4'] = '1'
     assert_equal @db.flush, @db
@@ -112,7 +112,7 @@
     @db.sync
 
     size = File.stat(DB_PATH).size
-    @db.compact
+    @db.compact(:force => true)
     assert_equal @db[1], 1
     assert size > File.stat(DB_PATH).size
   end
@@ -154,7 +154,7 @@
     @db.lock { 20.times {|i| @db[i] = i } }
     db2 = Daybreak::DB.new DB_PATH
     @db.lock { 20.times {|i| @db[i] = i } }
-    @db.compact
+    @db.compact(:force => true)
     db2.sync
     assert_equal 19, db2['19']
     db2.close
@@ -293,12 +293,12 @@
     end
     c = Thread.new do
       db = Daybreak::DB.new DB_PATH
-      db.compact until stop
+      db.compact(:force => true) until stop
       db.close
     end
     d = Thread.new do
       db = Daybreak::DB.new DB_PATH
-      db.compact until stop
+      db.compact(:force => true) until stop
       db.close
     end
     stop = true
@@ -318,7 +318,7 @@
     @db[1] = 2
     @db.lock do
       @db[1] = 2
-      @db.compact
+      @db.compact(:force => true)
     end
   end