PROBLEM TO BE SOLVED: To provide a method for acquiring a consistent snapshot when retaining data among a plurality of nodes in a distributed manner.SOLUTION: An inventive method includes: in response to receipt of a snapshot request from a first node that receives an instruction to acquire a snapshot, identifying transactions in progress; transmitting data representing states of the identified transactions in progress to the first node; after identifying the transactions in progress, performing a normal completion prevention processing to prevent the transactions in progress from normally completing; receiving a list of specific transactions of which results are reflected to snapshot data from the first node; and executing copy-on-write on a basis of a specific time after removing the specific transactions from among transactions to be processed in the normal completion prevention processing and confirming that all of the specific transactions are normally completed or cancelled.
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