Fixes

src/db_connector.py

@@ -3,7 +3,7 @@ Database connection layer with connection pooling for VideoDetect.
 
 Provides:
 - Connection pooling via DBUtils + PyMySQL
-- Automatic reconnection on disconnect
+- Automatic reconnection on disconnect (ping + retry on transient errors)
 - Context manager support
 - Prepared statements for all queries
 - Transaction support for atomic state transitions
@@ -11,6 +11,7 @@ Provides:
 
 import contextlib
 import logging
+import time
 from typing import Optional
 
 from dbutils.pooled_db import PooledDB
@@ -22,6 +23,12 @@ logger = logging.getLogger(__name__)
 class DBConnector:
     """Thread-safe database connection pool manager."""
 
+    # Transient errors that indicate a dropped/stale connection and are safe
+    # to retry with a fresh connection from the pool.
+    _RETRYABLE_ERRORS = (pymysql.err.InterfaceError, pymysql.err.OperationalError)
+    _MAX_RETRIES = 3
+    _RETRY_BACKOFF_SECONDS = 0.5
+
     def __init__(
         self,
         host: str = "mariadb",
@@ -41,9 +48,13 @@ class DBConnector:
             "maxcached": pool_size,
             "maxusage": 200,
             "blocking": True,
+            # ping(0) = check if connection is alive BEFORE returning it from
+            # the pool. This is the correct DBUtils mechanism for detecting
+            # dead/stale connections (idle timeout, network blip, DB restart).
+            "ping": 0,
         }
-        
-        # PyMySQL connection parameters  
+
+        # PyMySQL connection parameters
         connection_params = {
             "host": host,
             "port": port,
@@ -55,10 +66,11 @@ class DBConnector:
             "read_timeout": 30,
             "write_timeout": 30,
         }
-        
+
         self._pool = PooledDB(**pool_config, **connection_params)
+        self._pool_recycle = pool_recycle
         logger.info(
-            "DB pool initialized: host=%s db=%s pool_size=%d min=%d",
+            "DB pool initialized: host=%s db=%s pool_size=%d min=%d ping=0",
             host, database, pool_size, pool_min,
         )
 
@@ -66,10 +78,85 @@ class DBConnector:
         """Get a connection from the pool."""
         return self._pool.connection()
 
+    def _run_query(self, query: str, params, transaction: bool, fetch: str):
+        """Run a single query on a fresh connection, with retry on transient errors.
+
+        A pooled connection can be dropped by the server (idle timeout, network
+        blip, DB restart). When that happens the query fails with an
+        InterfaceError/OperationalError. We discard the dead connection and
+        retry with a fresh one from the pool.
+
+        Args:
+            query: SQL statement.
+            params: Bound parameters (or None).
+            transaction: If True, wrap the query in a transaction.
+            fetch: One of "none", "one", or "all" controlling the return value.
+
+        Returns:
+            - "none": the affected row count.
+            - "one": a single row (dict) or None.
+            - "all": a list of rows (dicts).
+        """
+        last_exc = None
+        for attempt in range(1, self._MAX_RETRIES + 1):
+            conn = self.get_connection()
+            try:
+                cursor = conn.cursor()
+                if transaction:
+                    conn.begin()
+                cursor.execute(query, params or ())
+                if fetch == "one":
+                    result = cursor.fetchone()
+                elif fetch == "all":
+                    result = cursor.fetchall()
+                else:
+                    result = cursor.rowcount
+                if transaction:
+                    conn.commit()
+                cursor.close()
+                conn.close()
+                return result
+            except self._RETRYABLE_ERRORS as e:
+                last_exc = e
+                logger.warning(
+                    "Transient DB error (attempt %d/%d): %s",
+                    attempt, self._MAX_RETRIES, e,
+                )
+                # Discard the dead connection; a fresh one is taken on retry.
+                self._safe_close(conn)
+                if attempt < self._MAX_RETRIES:
+                    time.sleep(self._RETRY_BACKOFF_SECONDS * attempt)
+            except Exception:
+                # Non-transient error: roll back if in a transaction and re-raise.
+                if transaction:
+                    self._safe_rollback(conn)
+                self._safe_close(conn)
+                raise
+        raise last_exc
+
+    @staticmethod
+    def _safe_close(conn):
+        try:
+            conn.close()
+        except Exception:
+            pass
+
+    @staticmethod
+    def _safe_rollback(conn):
+        try:
+            conn.rollback()
+        except Exception:
+            pass
+
     @contextlib.contextmanager
     def get_cursor(self, transaction: bool = False):
-        """Context manager for getting a cursor with optional transaction support."""
+        """Context manager for getting a cursor with optional transaction support.
+
+        Note: this does not retry on transient errors; use execute/fetchone/
+        fetchall for retry-safe single-statement queries.
+        """
         conn = self.get_connection()
+        cursor = None
         try:
             cursor = conn.cursor()
             if transaction:
@@ -79,11 +166,15 @@ class DBConnector:
                 conn.commit()
         except Exception:
             if transaction:
-                conn.rollback()
+                self._safe_rollback(conn)
             raise
         finally:
-            cursor.close()
-            conn.close()
+            if cursor is not None:
+                try:
+                    cursor.close()
+                except Exception:
+                    pass
+            self._safe_close(conn)
 
     @contextlib.contextmanager
     def transaction(self):
@@ -94,28 +185,22 @@ class DBConnector:
             yield conn
             conn.commit()
         except Exception:
-            conn.rollback()
+            self._safe_rollback(conn)
             raise
         finally:
-            conn.close()
+            self._safe_close(conn)
 
     def execute(self, query: str, params=None, transaction: bool = False):
-        """Execute a query and return affected rows."""
-        with self.get_cursor(transaction=transaction) as cursor:
-            cursor.execute(query, params or ())
-            return cursor.rowcount
+        """Execute a query and return affected rows. Retries on transient errors."""
+        return self._run_query(query, params, transaction, fetch="none")
 
     def fetchone(self, query: str, params=None):
-        """Execute a query and return one row."""
-        with self.get_cursor() as cursor:
-            cursor.execute(query, params or ())
-            return cursor.fetchone()
+        """Execute a query and return one row. Retries on transient errors."""
+        return self._run_query(query, params, transaction=False, fetch="one")
 
     def fetchall(self, query: str, params=None):
-        """Execute a query and return all rows."""
-        with self.get_cursor() as cursor:
-            cursor.execute(query, params or ())
-            return cursor.fetchall()
+        """Execute a query and return all rows. Retries on transient errors."""
+        return self._run_query(query, params, transaction=False, fetch="all")
 
     def initialize_schema(self, schema_path: str = "db/schema.sql"):
         """Initialize the database schema from SQL file."""