code: def _initialize_tables(engine):
      _logger.info("Creating initial MLflow database tables...")
      InitialBase.metadata.create_all(engine)
      _upgrade_db(engine)
  
imports: import logging
  import os
  import time
  from contextlib import contextmanager
  import sqlalchemy
  from alembic.migration import MigrationContext
  from alembic.script import ScriptDirectory
  from sqlalchemy import sql
  from sqlalchemy.pool import AssertionPool, AsyncAdaptedQueuePool, FallbackAsyncAdaptedQueuePool, NullPool, QueuePool, SingletonThreadPool, StaticPool
  from mlflow.environment_variables import MLFLOW_SQLALCHEMYSTORE_ECHO, MLFLOW_SQLALCHEMYSTORE_MAX_OVERFLOW, MLFLOW_SQLALCHEMYSTORE_POOL_RECYCLE, MLFLOW_SQLALCHEMYSTORE_POOL_SIZE, MLFLOW_SQLALCHEMYSTORE_POOLCLASS
  from mlflow.exceptions import MlflowException
  from mlflow.protos.databricks_pb2 import BAD_REQUEST, INTERNAL_ERROR, TEMPORARILY_UNAVAILABLE
  from mlflow.store.db.db_types import SQLITE
  from mlflow.store.model_registry.dbmodels.models import SqlModelVersion, SqlModelVersionTag, SqlRegisteredModel, SqlRegisteredModelAlias, SqlRegisteredModelTag
  from mlflow.store.tracking.dbmodels.initial_models import Base
  from mlflow.store.tracking.dbmodels.models import SqlDataset, SqlExperiment, SqlExperimentTag, SqlInput, SqlInputTag, SqlLatestMetric, SqlMetric, SqlParam, SqlRun, SqlTag
label_desc: Use image node_id 3 for calling a global function with example usage: _initialize_tables(engine) without return types