[GitHub] [hbase] Apache9 commented on a change in pull request #3405: HBASE-26011 Introduce a new API to sync the live region server list m…

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Apache9 commented on a change in pull request #3405:
URL: https://github.com/apache/hbase/pull/3405#discussion_r657159026



##########
File path: hbase-server/src/main/java/org/apache/hadoop/hbase/master/ServerManager.java
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@@ -163,6 +169,44 @@
   private final ConcurrentNavigableMap<ServerName, ServerMetrics> onlineServers =
     new ConcurrentSkipListMap<>();
 
+  /**
+   * Store the snapshot of the current region server list, for improving read performance.
+   * <p/>
+   * The hashCode is used to determine whether there are changes to the region servers.
+   */
+  private static final class OnlineServerListSnapshot {
+
+    private static final HashFunction HASH = Hashing.murmur3_128();
+
+    final List<ServerName> servers;
+
+    final long hashCode;
+
+    public OnlineServerListSnapshot(List<ServerName> servers) {
+      this.servers = Collections.unmodifiableList(servers);
+      Hasher hasher = HASH.newHasher();
+      for (ServerName server : servers) {
+        hasher.putString(server.getServerName(), StandardCharsets.UTF_8);
+      }
+      this.hashCode = hasher.hash().asLong();

Review comment:
       Ah, this is a problem. In real world, for the replication scenario, usually it is not a problem as it is not likely that a regionserver which can only live for less than 5 seconds could hold any regions. But consider general usage, maybe we should let users know there is a dead server.
   
   Let me think how to deal with this.




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