Provided are techniques for selecting row identifiers from an initial index structure storing rows of randomized indexes. The row identifiers are randomized. Groups are formed with the randomized row identifiers so that each group has a predetermined number of row identifiers. At least one group is selected from the groups. Indexes are retrieved from the initial index structure that correspond to the row identifiers in the selected at least one group. The retrieved indexes are encoded by adding product information to form new identifiers.