perf(core): cache SQLAlchemy engine per database URL to eliminate redundant TCP handshake

orchestrator/metastore/sql/utils.py

@@ -5,10 +5,29 @@
 
 from orchestrator.utilities.location import SQLStoreConfiguration
 
+# Process-level cache: reuse the same SQLAlchemy Engine (and its connection pool)
+# for every call with the same database URL.  This means the metastore and the
+# samplestore — which both point at the same MySQL server — share one pool and
+# avoid the overhead of opening a second TCP connection.
+_engine_cache: dict[str, sqlalchemy.Engine] = {}
+
 
 def engine_for_sql_store(
     configuration: SQLStoreConfiguration, database: str | None = None
 ) -> sqlalchemy.Engine:
+    """Return a SQLAlchemy Engine for the given store configuration.
+
+    Engines are cached by their connection URL so that multiple components
+    connecting to the same database reuse a single connection pool rather than
+    each opening their own TCP connection.
+
+    Args:
+        configuration: Database connection parameters.
+        database: Optional database name override.
+
+    Returns:
+        A (possibly cached) SQLAlchemy Engine.
+    """
     if configuration is None:
         raise ValueError("engine_for_sql_store requires a valid SQLStoreConfiguration")
 
@@ -27,6 +46,10 @@ def engine_for_sql_store(
         if configuration.scheme == "sqlite"
         else configuration.url().unicode_string()
     )
+
+    if db_location in _engine_cache:
+        return _engine_cache[db_location]
+
     engine_args: dict = {"echo": False}
     if configuration.scheme != "sqlite":
         # Prevent "Lost connection to MySQL server during query" (error 2013) when
@@ -39,7 +62,10 @@ def engine_for_sql_store(
         # Other components on the connection also may close the connection at
         # other unknown intervals
         # engine_args["pool_recycle"] = 1800
-    return sqlalchemy.create_engine(db_location, **engine_args)
+
+    engine = sqlalchemy.create_engine(db_location, **engine_args)
+    _engine_cache[db_location] = engine
+    return engine
 
 
 def create_sql_resource_store(engine: sqlalchemy.Engine) -> sqlalchemy.Engine: