code: def _get_alembic_config(db_url, alembic_dir=None):
      """
      Constructs an alembic Config object referencing the specified database and migration script
      directory.
  
      :param db_url Database URL, like sqlite:///<absolute-path-to-local-db-file>. See
      https://docs.sqlalchemy.org/en/13/core/engines.html#database-urls for a full list of valid
      database URLs.
      :param alembic_dir Path to migration script directory. Uses canonical migration script
      directory under mlflow/alembic if unspecified. TODO: remove this argument in MLflow 1.1, as
      it's only used to run special migrations for pre-1.0 users to remove duplicate constraint
      names.
      """
      from alembic.config import Config
  
      final_alembic_dir = (
          os.path.join(_get_package_dir(), "store", "db_migrations")
          if alembic_dir is None
          else alembic_dir
      )
      # Escape any '%' that appears in a db_url. This could be in a password,
      # url, or anything that is part of a potentially complex database url
      db_url = db_url.replace("%", "%%")
      config = Config(os.path.join(final_alembic_dir, "alembic.ini"))
      config.set_main_option("script_location", final_alembic_dir)
      config.set_main_option("sqlalchemy.url", db_url)
      return config
  
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 7 for calling a global function with example usage: _get_alembic_config(db_url, alembic_dir) and returns: config