【平台使用】性能告警cannot map directly to c-types

请问：在回测时报性能告警，是什么原因，如何避免？

/usr/local/python3/lib/python3.8/site-packages/pandas/core/generic.py:2605: PerformanceWarning:

your performance may suffer as PyTables will pickle object types that it cannot

map directly to c-types [inferred_type->mixed,key->block3_values] [items->Index(['instrument', 'name', 'suspend_type', 'suspend_reason', 'suspended'], dtype='object')]

pytables.to_hdf(