Downgrade assets db by removing the 'tick_size' column and renaming the
    'multiplier' column.

def _downgrade_v1(op):
    """
    Downgrade assets db by removing the 'tick_size' column and renaming the
    'multiplier' column.
    """
    # Drop indices before batch
    # This is to prevent index collision when creating the temp table
    op.drop_index('ix_futures_contracts_root_symbol')
    op.drop_index('ix_futures_contracts_symbol')

    # Execute batch op to allow column modification in SQLite
    with op.batch_alter_table('futures_contracts') as batch_op:

        # Rename 'multiplier'
        batch_op.alter_column(column_name='multiplier',
                              new_column_name='contract_multiplier')

        # Delete 'tick_size'
        batch_op.drop_column('tick_size')

    # Recreate indices after batch
    op.create_index('ix_futures_contracts_root_symbol',
                    table_name='futures_contracts',
                    columns=['root_symbol'])
    op.create_index('ix_futures_contracts_symbol',
                    table_name='futures_contracts',
                    columns=['symbol'],
                    unique=True)