A method for calculating a size of a processing unit in a system, the system being configured to perform a reflection process that includes reflecting information on an operation performed in a row-type database on a column-type database in a predetermined processing unit, the method includes: executing a first calculation process for calculating a reference value based on processing costs of multi-version concurrency control performed in the processing unit by the database management system and information on processing costs of a process of converting the information on the operation performed in the row-type database into a form of the column-type database after the reflection process is executed in a previous time; and executing a second calculation process for calculating a size of a processing unit based on the reference value calculated by the first calculation process and information on a deviation of the number of valid rows.
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