Apparatus and method for processing a query

An apparatus configured to process a query for a NoSQL database, the apparatus comprising:

• a storage unit configured to store (i) a plurality of safe elements committed and saved in the database, (ii) a plurality of unsafe elements configured to update the plurality of safe elements, the unsafe elements being not committed or saved without a transaction state of committed, and (iii) a plurality of pieces of identification information configured to identify a plurality of transactions relating to updating the plurality of safe elements with the plurality of unsafe elements in association with one another;
• a first query executing unit configured to execute the query on the plurality of unsafe elements, and to include in a result of the query, a specific unsafe element extracted using the query among the plurality of unsafe elements if a state of transaction identified by the identification information among the plurality of pieces of identification information stored in association with the specific unsafe element satisfies a predetermined condition of the query;
• a second query executing unit configured to execute the query on the plurality of safe elements after the first query executing unit executes the query, and to include in a result of the query, a specific safe element extracted using the query among the plurality of safe elements if a state of transaction identified by the identification information among the plurality of pieces of identification information stored in association with the specific safe element satisfies the predetermined condition of the query;
• and
• a third query executing unit configured to execute the query on at least one safe element saved during execution of the query by the second query executing unit after the second query executing unit executes the query, and to include in a result of the query, a specific safe element extracted using the query among the at least one safe element if a state of transaction identified by the identification information among the plurality of pieces of identification information stored in association with the specific safe element satisfies the predetermined condition of the query.