1. A transaction system comprising: a key value data storage unit which stores 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 storage unit which stores 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 which, in commit of the transaction, determines presence or absence of exclusion violation per record on a basis of the update history stored in the WAL storage unit and, in a case where exclusion violation is absent, makes the transaction succeed and records the update history relating to the transaction into the WAL storage unit; and a WAL reflection processing unit which updates the key value data storage unit on the basis of the update history stored in the WAL storage unit.