Remove NullPool default, use QueuePool for network database

NullPool creates a new TCP connection per operation which is expensive
for a network database like dqlite. Remove the get_pool_class override
to let SQLAlchemy use its default QueuePool, matching the pattern used
by PostgreSQL and MySQL dialects.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: antoineleclair

src/sqlalchemydqlite/base.py

@@ -2,7 +2,6 @@
 
 from typing import Any
 
-from sqlalchemy import pool
 from sqlalchemy.dialects.sqlite.base import SQLiteDialect
 from sqlalchemy.engine import URL
 from sqlalchemy.engine.interfaces import DBAPIConnection, IsolationLevel
@@ -23,11 +22,6 @@ class DqliteDialect(SQLiteDialect):
     # Enable SQLAlchemy statement caching
     supports_statement_cache = True
 
-    # Default to NullPool since dqlite handles connection pooling internally
-    @classmethod
-    def get_pool_class(cls, url: URL) -> type[pool.Pool]:
-        return pool.NullPool
-
     @classmethod
     def import_dbapi(cls) -> Any:
         import dqlitedbapi

tests/test_dialect.py

@@ -378,6 +378,20 @@ def test_ping_closes_cursor_even_on_error(self) -> None:
         mock_cursor.close.assert_called_once()
 
 
+class TestPoolClass:
+    def test_sync_dialect_does_not_use_nullpool(self) -> None:
+        """Sync dialect should not default to NullPool for a network database."""
+        from sqlalchemy import pool
+        from sqlalchemy.engine import URL
+
+        url = URL.create("dqlite", host="localhost", port=9001, database="test")
+        pool_class = DqliteDialect.get_pool_class(url)
+        assert pool_class is not pool.NullPool, (
+            "NullPool creates a new TCP connection per operation; "
+            "a network database should use QueuePool"
+        )
+
+
 class TestURLParsing:
     def test_parse_basic_url(self) -> None:
         url = URL.create("dqlite", host="localhost", port=9001, database="test")