[GitHub] [hbase] virajjasani commented on a change in pull request #3438: HBASE-22923 min version of RegionServer to move system table regions

[GitBox <gi...@apache.org>]

virajjasani commented on a change in pull request #3438:
URL: https://github.com/apache/hbase/pull/3438#discussion_r662179581



##########
File path: hbase-server/src/main/java/org/apache/hadoop/hbase/master/AssignmentManager.java
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@@ -2551,19 +2566,44 @@ private int setOfflineInZooKeeper(final RegionState state, final ServerName dest
    * know the version. So in fact we will never assign a system region to a RS without registering on zk.
    */
   public List<ServerName> getExcludedServersForSystemTable() {
+    return getExcludedServersForSystemTable(false);
+  }
+
+  /**
+   * Get a list of servers that this region can not assign to.
+   * For system table, we must assign them to a server with highest version.
+   * We can disable this exclusion using config:
+   * "hbase.min.version.move.system.tables" if checkForMinVersion is true.
+   *
+   * @param checkForMinVersion if true, check for minVersionToMoveSysTables
+   *   and decide moving system table regions accordingly.
+   * @return List of Excluded servers for System table regions.
+   */
+  private List<ServerName> getExcludedServersForSystemTable(
+      boolean checkForMinVersion) {
     List<Pair<ServerName, String>> serverList = new ArrayList<>();
     for (ServerName s : serverManager.getOnlineServersList()) {
       serverList.add(new Pair<>(s, server.getRegionServerVersion(s)));
     }
     if (serverList.isEmpty()) {
-      return new ArrayList<>();
+      return Collections.emptyList();
     }
-    String highestVersion = Collections.max(serverList, new Comparator<Pair<ServerName, String>>() {
+    String highestVersion = Collections.max(serverList,
+        new Comparator<Pair<ServerName, String>>() {
       @Override
       public int compare(Pair<ServerName, String> o1, Pair<ServerName, String> o2) {
         return VersionInfo.compareVersion(o1.getSecond(), o2.getSecond());
       }
     }).getSecond();
+    if (checkForMinVersion) {
+      if (!DEFAULT_MIN_VERSION_MOVE_SYS_TABLES_CONFIG.equals(minVersionToMoveSysTables)) {

Review comment:
       Love these discussions, always learn a thing or two :)
   
   `decisionFactor = decisionFactor && additionalFactors` yeah, this is also nice way. I wish we had some standards around this.
   For now, let me keep it as is as you don't have strong opinion, I still find this simpler:
   ```
     if (decisionFactor) {
       if (additionalFactors) {
       }
     }
   ```
   I think this is why we don't have standards because individuals find different approaches as simpler ones than others (but CPU doesn't care :) )




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