private boolean modNeedsKey(DiskEntry entry) {
    DiskId did = entry.getDiskId();
    synchronized (did) {
      // the last record for it was written in a different oplog
      // so we need the key.
      return did.getOplogId() != getOplogId();
    }
  }
Returns true if the given entry has not yet been written to this oplog.
geode-core/src/main/java/org/apache/geode/internal/cache/Oplog.java