@Override public List<String> getCatalogs() {
    // in case of event based cache update, cache will not be updated for catalog.
    if (!sharedCache.isCatalogCachePrewarmed() || canUseEvents) {
      return rawStore.getCatalogs();
    }
    return sharedCache.listCachedCatalogs();
  }
This starts a background thread, which initially populates the SharedCache and later
periodically gets updates from the metastore db

@param conf
@param runOnlyOnce
@param shouldRunPrewarm
standalone-metastore/metastore-server/src/main/java/org/apache/hadoop/hive/metastore/cache/CachedStore.java