1. A transaction system comprising: a key value data storage unit configured to store a plurality of key value data, each of the key value data being a pair of key and value, the value containing a record of tabular data including a plurality of rows or records, and the key containing part of column values of the record contained in the value; a WAL (Write Ahead log) storage unit configured to store an update history of a data group, the data group including the plurality of key value data to be referred to and updated by one transaction, and the update history having information of a data manipulation instruction in the transaction and the record after changed through processing according to the data manipulation instruction; a transaction processing unit configured to, in commit of the transaction, determine presence or absence of exclusion violation per record on a basis of the update history stored in the WAL (Write Ahead log) storage unit and, in a case where exclusion violation is absent, make the transaction succeed and record the update history relating to the transaction into the WAL (Write Ahead log) storage unit; and a WAL (Write Ahead log) reflection processing unit configured to update the key value data storage unit on the basis of the update history stored in the WAL (Write Ahead log) storage unit.