default void preMemStoreCompaction(ObserverContext<? extends RegionCoprocessorEnvironment> c,
    Store store) throws IOException {
  }
Called before in memory compaction started.
@param c     the environment provided by the region server
@param store the store where in memory compaction is being requested
hbase-server/src/main/java/org/apache/hadoop/hbase/coprocessor/RegionObserver.java