private Region<String, Integer> getEventIdIndexMetaDataRegion() {
    if (eventIdIndexMetaDataRegion == null) {
      eventIdIndexMetaDataRegion = initializeEventIdIndexMetaDataRegion(this);
    }
    return eventIdIndexMetaDataRegion;
  }
During sender is getting stopped, if there are any cache operation on queue then that event
will be stored in temp queue. Once sender is started, these event from tmp queue will be
cleared.
geode-core/src/main/java/org/apache/geode/internal/cache/wan/AbstractGatewaySender.java