public Optional<byte[]> getSplitPoint() {
    this.storeEngine.readLock();
    try {
      // Should already be enforced by the split policy!
      assert !this.getRegionInfo().isMetaRegion();
      // Not split-able if we find a reference store file present in the store.
      if (hasReferences()) {
        LOG.trace("Not splittable; has references: {}", this);
        return Optional.empty();
      }
      return this.storeEngine.getStoreFileManager().getSplitPoint();
    } catch (IOException e) {
      LOG.warn("Failed getting store size for {}", this, e);
    } finally {
      this.storeEngine.readUnlock();
    }
    return Optional.empty();
  }
Determines if Store should be split.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/HStore.java