code: public void clearUnused() {
          if (tc.isEntryEnabled())
              Tr.entry(tc, "clearUnused");
  
          final RecoveryLog partnerLog = _failureScopeController.getPartnerLog();
  
          _pltWriteLock.lock();
  
          try {
              boolean cleared = false;
  
              for (PartnerLogData pld : _partnerLogTable) {
                  cleared |= pld.clearIfNotInUse();
              }
  
              try {
                  if (cleared) {
                      ((DistributedRecoveryLog) partnerLog).keypoint();
                  }
              } catch (Exception exc) {
                  // The keypoint operation has failed. There is very little we can do
                  // other than continue with the close logic. This should be the the
                  // that access to the log. There is nothing helpfull we can do at
                  // this point.
              }
          } finally {
              _pltWriteLock.unlock();
          }
  
          if (tc.isEntryEnabled())
              Tr.exit(tc, "clearUnused");
      }
docs: Scans through the partners listed in this table and instructs each of them to clear themselves from
  the recovery log if they are not associated with current transactions. Entries remain in the table
  an can be re-logged during if they are used again.