fix overestimation

Co-authored-by: Jordan Powers <[email protected]>

Author: martijnvg

server/src/main/java/org/elasticsearch/index/engine/Engine.java

@@ -315,7 +315,7 @@ protected static ShardFieldStats shardFieldStats(List<LeafReaderContext> leaves)
                             // This almost does what FixedBitSet#ramBytesUsed() does, liveDocs.length() returns the length of the bits long
                             // array
                             liveDocsBytes += RamUsageEstimator.alignObjectSize(
-                                (long) RamUsageEstimator.NUM_BYTES_ARRAY_HEADER + (long) Long.BYTES * liveDocs.length()
+                                (long) RamUsageEstimator.NUM_BYTES_ARRAY_HEADER + (long)(liveDocs.length() / 8)
                             );
                         }
                     }