Patent attributes
A KV data storage part stores a plurality of key value data each being a pair of key and value. The value contains a record of tabular data. The key contains part of column values of the record. A WAL storage part stores an update history of a data group. The data group includes a plurality of KV data referred to and updated by one transaction. The update history has information of a data manipulation instruction in the transaction and the record changed through processing according to the data manipulation instruction. A transaction processor, in commit of the transaction, determines the presence or absence of exclusion violation per record on a basis of the update history stored in the WAL storage part and, if exclusion violation is absent, makes the transaction succeed and records the update history relating to the transaction into the WAL storage part.