improve deadlock detection for various versions of psycopg2

[nominatim.git] / nominatim / db / async_connection.py

diff --git a/nominatim/db/async_connection.py b/nominatim/db/async_connection.py
index 45e83664663ba835419db49304209b9da6491d35..c5d6872bf0790abfaa10f7b07d2567ba0913663d 100644 (file)
--- a/nominatim/db/async_connection.py
+++ b/nominatim/db/async_connection.py
@@ -9,8 +9,41 @@ import logging
 import psycopg2
 from psycopg2.extras import wait_select
 
+# psycopg2 emits different exceptions pre and post 2.8. Detect if the new error
+# module is available and adapt the error handling accordingly.
+try:
+    import psycopg2.errors # pylint: disable=no-name-in-module,import-error
+    __has_psycopg2_errors__ = True
+except ModuleNotFoundError:
+    __has_psycopg2_errors__ = False
+
 LOG = logging.getLogger()
 
+class DeadlockHandler:
+    """ Context manager that catches deadlock exceptions and calls
+        the given handler function. All other exceptions are passed on
+        normally.
+    """
+
+    def __init__(self, handler):
+        self.handler = handler
+
+    def __enter__(self):
+        pass
+
+    def __exit__(self, exc_type, exc_value, traceback):
+        if __has_psycopg2_errors__:
+            if exc_type == psycopg2.errors.DeadlockDetected: # pylint: disable=E1101
+                self.handler()
+                return True
+        else:
+            if exc_type == psycopg2.extensions.TransactionRollbackError:
+                if exc_value.pgcode == '40P01':
+                    self.handler()
+                    return True
+        return False
+
+
 class DBConnection:
     """ A single non-blocking database connection.
     """
@@ -24,15 +57,22 @@ class DBConnection:
         self.cursor = None
         self.connect()
 
+    def close(self):
+        """ Close all open connections. Does not wait for pending requests.
+        """
+        if self.conn is not None:
+            self.cursor.close()
+            self.conn.close()
+
+        self.conn = None
+
     def connect(self):
         """ (Re)connect to the database. Creates an asynchronous connection
             with JIT and parallel processing disabled. If a connection was
             already open, it is closed and a new connection established.
             The caller must ensure that no query is pending before reconnecting.
         """
-        if self.conn is not None:
-            self.cursor.close()
-            self.conn.close()
+        self.close()
 
         # Use a dict to hand in the parameters because async is a reserved
         # word in Python3.
@@ -50,23 +90,18 @@ class DBConnection:
                    WHERE name = 'max_parallel_workers_per_gather';""")
         self.wait()
 
+    def _deadlock_handler(self):
+        LOG.info("Deadlock detected (params = %s), retry.", str(self.current_params))
+        self.cursor.execute(self.current_query, self.current_params)
+
     def wait(self):
         """ Block until any pending operation is done.
         """
         while True:
-            try:
+            with DeadlockHandler(self._deadlock_handler):
                 wait_select(self.conn)
                 self.current_query = None
                 return
-            except psycopg2.extensions.TransactionRollbackError as error:
-                if error.pgcode == '40P01':
-                    LOG.info("Deadlock detected (params = %s), retry.",
-                             str(self.current_params))
-                    self.cursor.execute(self.current_query, self.current_params)
-                else:
-                    raise
-            except psycopg2.errors.DeadlockDetected: # pylint: disable=E1101
-                self.cursor.execute(self.current_query, self.current_params)
 
     def perform(self, sql, args=None):
         """ Send SQL query to the server. Returns immediately without
@@ -90,17 +125,9 @@ class DBConnection:
         if self.current_query is None:
             return True
 
-        try:
+        with DeadlockHandler(self._deadlock_handler):
             if self.conn.poll() == psycopg2.extensions.POLL_OK:
                 self.current_query = None
                 return True
-        except psycopg2.extensions.TransactionRollbackError as error:
-            if error.pgcode == '40P01':
-                LOG.info("Deadlock detected (params = %s), retry.", str(self.current_params))
-                self.cursor.execute(self.current_query, self.current_params)
-            else:
-                raise
-        except psycopg2.errors.DeadlockDetected: # pylint: disable=E1101
-            self.cursor.execute(self.current_query, self.current_params)
 
         return False