The present invention provides a method for performing transactions on data entities in a database and a transactional database. The database comprises an ordered set of data stores with at least one static data store, wherein said static data store uses an index structure based on a non-updatable representation of an ordered set of integers according to the principle of compressed inverted indices. The method allows to generate a modifiable data store when the performed transaction comprises an insert, update or delete operation, to execute operations of the transaction on the ordered set being present at the time when the transaction has been started and, if present, on the modifiable data store and to convert data stores to a new static data store, The insert, update or delete operation are executed on the modifiable data store which is the only data store modifiable for the transaction.