public void incTombstoneCount(int delta) {
    // Synchronize on this to prevent changing the value in the middle of a size count
    // see getRegionSize method and RegionSizeIntegrationTest
    synchronized (tombstoneCount) {
      tombstoneCount.addAndGet(delta);
    }
    cachePerfStats.incTombstoneCount(delta);

    // don't include the tombstones in any of our entry count stats
    cachePerfStats.incEntryCount(-delta);
  }
regions track the number of tombstones their map holds for size calculations
geode-core/src/main/java/org/apache/geode/internal/cache/LocalRegion.java