HDFS-16257. Set initialCapacity for guava cache to solve performance issue (#3524)

* HDFS-16257. Set initialCapacity for guava cache to solve performance issue

* HDFS-16257. Add comments

Co-authored-by: Symious <yiyang0203@gmail.com>

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/resolver/MountTableResolver.java

@@ -138,6 +138,9 @@ public class MountTableResolver
           FEDERATION_MOUNT_TABLE_MAX_CACHE_SIZE,
           FEDERATION_MOUNT_TABLE_MAX_CACHE_SIZE_DEFAULT);
       this.locationCache = CacheBuilder.newBuilder()
+          // To workaround guava bug https://github.com/google/guava/issues/1055
+          // Fixed since guava 13.0
+          .initialCapacity(maxCacheSize)
           .maximumSize(maxCacheSize)
           .build();
     } else {