Implement optional database VACUUM on shutdown

Disabled by default.

Closes #80.

Author: eht16

docs/config.rst

@@ -375,6 +375,16 @@ for easy modification.
     *Default*: None
 
 
+``constants.DATABASE_VACUUM_ON_SHUTDOWN``
+
+    Vacuum SQLite database on shutdown - when enabled, the database will be vacuumed on shutdown
+    to reduce its size on disk.
+
+    *Type*: ``boolean``
+
+    *Default*: False
+
+
 Example usage:
 
 .. code-block:: python

logstash_async/constants.py

@@ -47,6 +47,9 @@ class Constants:
     # Use a string like '5 per minute' or None to disable (default), for details see
     # http://limits.readthedocs.io/en/stable/string-notation.html
     ERROR_LOG_RATE_LIMIT = None
+    # Vacuum SQLite database on shutdown - when enabled, the database will be vacuumed on shutdown
+    # to reduce its size on disk
+    DATABASE_VACUUM_ON_SHUTDOWN = False
 
 
 constants = Constants()  # pylint: disable=invalid-name

logstash_async/database.py

@@ -152,3 +152,9 @@ def expire_events(self):
         with self._connect() as connection:
             cursor = connection.cursor()
             cursor.execute(query_delete)
+
+    # ----------------------------------------------------------------------
+    def vacuum(self):
+        with self._connect() as connection:
+            cursor = connection.cursor()
+            cursor.execute("VACUUM;")

logstash_async/worker.py

@@ -97,6 +97,7 @@ def run(self):
             self._log_general_error(exc)
         # check for empty queue and report if not
         self._warn_about_non_empty_queue_on_shutdown()
+        self._vaccum_database()
 
     # ----------------------------------------------------------------------
     def force_flush_queued_events(self):
@@ -357,3 +358,13 @@ def _warn_about_non_empty_queue_on_shutdown(self):
                 f'Non-empty queue while shutting down ({queue_size} events pending). '
                 'This indicates a previous error.',
                 extra=dict(queue_size=queue_size))
+
+    # ----------------------------------------------------------------------
+    def _vaccum_database(self):
+        if not constants.DATABASE_VACUUM_ON_SHUTDOWN:
+            return
+
+        try:
+            self._database.vacuum()
+        except DatabaseLockedError:
+            self._safe_log('debug', 'Database is locked, ignore vacuuming database')