somandal commented on code in PR #16791:
URL: https://github.com/apache/pinot/pull/16791#discussion_r2356715451


##########
pinot-broker/src/main/java/org/apache/pinot/broker/routing/BrokerRoutingManager.java:
##########
@@ -156,66 +185,85 @@ public synchronized void processClusterChange(ChangeType 
changeType) {
   }
 
   private void processSegmentAssignmentChange() {
-    LOGGER.info("Processing segment assignment change");
-    long startTimeMs = System.currentTimeMillis();
-
-    int numTables = _routingEntryMap.size();
-    if (numTables == 0) {
-      LOGGER.info("No table exists in the routing, skipping processing segment 
assignment change");
-      return;
-    }
-
-    List<RoutingEntry> routingEntries = new ArrayList<>(numTables);
-    List<String> idealStatePaths = new ArrayList<>(numTables);
-    List<String> externalViewPaths = new ArrayList<>(numTables);
-    for (Map.Entry<String, RoutingEntry> entry : _routingEntryMap.entrySet()) {
-      routingEntries.add(entry.getValue());
-      idealStatePaths.add(entry.getValue()._idealStatePath);
-      externalViewPaths.add(entry.getValue()._externalViewPath);
-    }
-    Stat[] idealStateStats = _zkDataAccessor.getStats(idealStatePaths, 
AccessOption.PERSISTENT);
-    Stat[] externalViewStats = _zkDataAccessor.getStats(externalViewPaths, 
AccessOption.PERSISTENT);
-    long fetchStatsEndTimeMs = System.currentTimeMillis();
-
-    List<String> tablesToUpdate = new ArrayList<>();
-    for (int i = 0; i < numTables; i++) {
-      Stat idealStateStat = idealStateStats[i];
-      Stat externalViewStat = externalViewStats[i];
-      if (idealStateStat != null && externalViewStat != null) {
-        RoutingEntry routingEntry = routingEntries.get(i);
-        if (idealStateStat.getVersion() != 
routingEntry.getLastUpdateIdealStateVersion()
-            || externalViewStat.getVersion() != 
routingEntry.getLastUpdateExternalViewVersion()) {
-          String tableNameWithType = routingEntry.getTableNameWithType();
-          tablesToUpdate.add(tableNameWithType);
-          try {
-            IdealState idealState = 
getIdealState(routingEntry._idealStatePath);
-            if (idealState == null) {
-              LOGGER.warn("Failed to find ideal state for table: {}, skipping 
updating routing entry",
-                  tableNameWithType);
-              continue;
-            }
-            ExternalView externalView = 
getExternalView(routingEntry._externalViewPath);
-            if (externalView == null) {
-              LOGGER.warn("Failed to find external view for table: {}, 
skipping updating routing entry",
-                  tableNameWithType);
-              continue;
+    _globalLock.readLock().lock();
+    try {
+      LOGGER.info("Processing segment assignment change");
+      long startTimeMs = System.currentTimeMillis();
+
+      Map<String, RoutingEntry> routingEntrySnapshot = new 
HashMap<>(_routingEntryMap);
+
+      int numTables = routingEntrySnapshot.size();
+      if (numTables == 0) {
+        LOGGER.info("No table exists in the routing, skipping processing 
segment assignment change");
+        return;
+      }
+
+      List<RoutingEntry> routingEntries = new ArrayList<>(numTables);
+      List<String> idealStatePaths = new ArrayList<>(numTables);
+      List<String> externalViewPaths = new ArrayList<>(numTables);
+      for (Map.Entry<String, RoutingEntry> entry : 
routingEntrySnapshot.entrySet()) {
+        routingEntries.add(entry.getValue());
+        idealStatePaths.add(entry.getValue()._idealStatePath);
+        externalViewPaths.add(entry.getValue()._externalViewPath);
+      }
+      Stat[] idealStateStats = _zkDataAccessor.getStats(idealStatePaths, 
AccessOption.PERSISTENT);
+      Stat[] externalViewStats = _zkDataAccessor.getStats(externalViewPaths, 
AccessOption.PERSISTENT);
+      long fetchStatsEndTimeMs = System.currentTimeMillis();
+
+      List<String> tablesToUpdate = new ArrayList<>();
+      for (int i = 0; i < numTables; i++) {
+        Stat idealStateStat = idealStateStats[i];
+        Stat externalViewStat = externalViewStats[i];
+        if (idealStateStat != null && externalViewStat != null) {
+          RoutingEntry cachedRoutingEntry = routingEntries.get(i);
+          // The routingEntry may have been removed from the _routingEntryMap 
by the time we get here in case
+          // one of the other functions such as 'removeRouting' was called 
since taking the snapshot. Check for
+          // existence before proceeding. Also note that if new entries were 
added since the snapshot was taken, we

Review Comment:
   discussed offline that we can perhaps do an additional check in buildRouting 
to see if the IS / EV changed in case the `processSegmentAssignmentChange()` 
code ran at the same time (basically by comparing timestamps and comparing 
EV/IS versions)
   
   I put the above in a do - while loop, so even if 
`processSegmentAssignmentChange()` runs many times, we should keep trying to 
update the `buildRouting` entry in that case. let me know what you think



##########
pinot-broker/src/main/java/org/apache/pinot/broker/routing/BrokerRoutingManager.java:
##########
@@ -109,12 +116,25 @@ public class BrokerRoutingManager implements 
RoutingManager, ClusterChangeHandle
   private final BrokerMetrics _brokerMetrics;
   private final Map<String, RoutingEntry> _routingEntryMap = new 
ConcurrentHashMap<>();
   private final Map<String, ServerInstance> _enabledServerInstanceMap = new 
ConcurrentHashMap<>();
-  // NOTE: _excludedServers doesn't need to be concurrent because it is only 
accessed within the synchronized block
-  private final Set<String> _excludedServers = new HashSet<>();
+  // Thread-safe set because it can be read/modified concurrently from 
instance/server change paths
+  private final Set<String> _excludedServers = ConcurrentHashMap.newKeySet();

Review Comment:
   done



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