Carry over version map size to prevent excessive resizing

core/src/main/java/org/elasticsearch/common/util/concurrent/ConcurrentCollections.java

@@ -43,7 +43,14 @@ public abstract class ConcurrentCollections {
      * Creates a new CHM with an aggressive concurrency level, aimed at high concurrent update rate long living maps.
      */
     public static <K, V> ConcurrentMap<K, V> newConcurrentMapWithAggressiveConcurrency() {
-        return new ConcurrentHashMap<>(16, 0.75f, aggressiveConcurrencyLevel);
+        return newConcurrentMapWithAggressiveConcurrency(16);
+    }
+
+    /**
+     * Creates a new CHM with an aggressive concurrency level, aimed at high concurrent update rate long living maps.
+     */
+    public static <K, V> ConcurrentMap<K, V> newConcurrentMapWithAggressiveConcurrency(int initalCapacity) {
+        return new ConcurrentHashMap<>(initalCapacity, 0.75f, aggressiveConcurrencyLevel);
     }
 
     public static <K, V> ConcurrentMap<K, V> newConcurrentMap() {

core/src/main/java/org/elasticsearch/index/engine/LiveVersionMap.java

@@ -102,7 +102,7 @@ public void beforeRefresh() throws IOException {
         // map.  While reopen is running, any lookup will first
         // try this new map, then fallback to old, then to the
         // current searcher:
-        maps = new Maps(ConcurrentCollections.<BytesRef,VersionValue>newConcurrentMapWithAggressiveConcurrency(), maps.current);
+        maps = new Maps(ConcurrentCollections.newConcurrentMapWithAggressiveConcurrency(maps.current.size()), maps.current);
 
         // This is not 100% correct, since concurrent indexing ops can change these counters in between our execution of the previous
         // line and this one, but that should be minor, and the error won't accumulate over time:
@@ -117,7 +117,7 @@ public void afterRefresh(boolean didRefresh) throws IOException {
         // case.  This is because we assign new maps (in beforeRefresh) slightly before Lucene actually flushes any segments for the
         // reopen, and so any concurrent indexing requests can still sneak in a few additions to that current map that are in fact reflected
         // in the previous reader.   We don't touch tombstones here: they expire on their own index.gc_deletes timeframe:
-        maps = new Maps(maps.current, ConcurrentCollections.<BytesRef,VersionValue>newConcurrentMapWithAggressiveConcurrency());
+        maps = new Maps(maps.current, Collections.emptyMap());
     }
 
     /** Returns the live version (add or delete) for this uid. */