public Transaction createWriteActiveTransactionInOldFormat(Transaction transaction, ApplicationId applicationId, long sessionId) {
        String path = applicationPath(applicationId).getAbsolute();
        return transaction.add(setData(path, Utf8.toAsciiBytes(sessionId)));
    }
Returns a transaction which writes the given session id as the currently active for the given application.

@param applicationId An {@link ApplicationId} that represents an active application.
@param sessionId session id belonging to the application package for this application id.
configserver/src/main/java/com/yahoo/vespa/config/server/application/ApplicationCuratorDatabase.java