setting an exclusive modification authority of a first instance for a first data block corresponding to a first transaction of the first instance, wherein the first data block is related to a first index node group including index nodes which participate in an index structure change which occurs by the first transaction;

verifying the exclusive modification authority of a second data block corresponding to a second transaction of a second instance, wherein the second data block is related to a second index node group including index nodes which participate in the index structure change which occurs by the second transaction; and

when the exclusive modification authority of the first instance for at least a part of the second data block is identified, making an access of the second transaction of modifying a data block in which the exclusive modification authority of the first instance is set in the second data block be waited until when the exclusive modification authority of the first instance is released, wherein the exclusive modification authority of the first instance remains until when the index structure change of the index nodes included in the first index group has been completed, and wherein index nodes which participate in the index structure change are grouped into one or more groups and an exclusive modification authority of each of groups is managed by each of a plurality of instances.