default void preMemStoreCompactionCompactScannerOpen(
    ObserverContext<? extends RegionCoprocessorEnvironment> c, Store store, ScanOptions options)
    throws IOException {
  }
Called before we open store scanner for in memory compaction. You can use the {@code options}
to change max versions and TTL for the scanner being opened. Notice that this method will only
be called when you use {@code eager} mode. For {@code basic} mode we will not drop any cells
thus we do not open a store scanner.
@param c       the environment provided by the region server
@param store   the store where in memory compaction is being requested
@param options used to change max versions and TTL for the scanner being opened
hbase-server/src/main/java/org/apache/hadoop/hbase/coprocessor/RegionObserver.java