From f66adb0278aa56e8c2696db6f3fe24d311bf7b44 Mon Sep 17 00:00:00 2001
From: Stefan Miklosovic <smiklosovic@apache.org>
Date: Tue, 23 May 2023 10:58:17 +0200
Subject: [PATCH] Remove unnecessary shuffling of GossipDigests in
 Gossiper#makeRandomGossipDigest

This patch also fixes the bug when creating GossipDigests in case epState in
Gossiper#makeRandomGossipDigest was null. Previously, if it was null, it used
generation and maxVersion of the last non-null epState instead of zeros.

patch by Cameron Zemek; reviewed by Stefan Miklosovic and Brandon Williams for CASSANDRA-18546
---
 CHANGES.txt                                   |  1 +
 .../org/apache/cassandra/gms/Gossiper.java    | 33 ++++++++-----------
 2 files changed, 14 insertions(+), 20 deletions(-)

diff --git a/CHANGES.txt b/CHANGES.txt
index 1923eb004c..786a8a6c92 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -1,4 +1,5 @@
 4.0.11
+ * Remove unnecessary shuffling of GossipDigests in Gossiper#makeRandomGossipDigest (CASSANDRA-18546)
 Merged from 3.11:
 Merged from 3.0:
 
diff --git a/src/java/org/apache/cassandra/gms/Gossiper.java b/src/java/org/apache/cassandra/gms/Gossiper.java
index ed5788e6ba..17e315a109 100644
--- a/src/java/org/apache/cassandra/gms/Gossiper.java
+++ b/src/java/org/apache/cassandra/gms/Gossiper.java
@@ -34,7 +34,6 @@ import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.Iterables;
 import com.google.common.collect.ImmutableSet;
-import com.google.common.collect.Iterables;
 import com.google.common.collect.Sets;
 import com.google.common.util.concurrent.ListenableFutureTask;
 import com.google.common.util.concurrent.Uninterruptibles;
@@ -52,7 +51,6 @@ import org.apache.cassandra.utils.Pair;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-import io.netty.util.concurrent.FastThreadLocal;
 import org.apache.cassandra.concurrent.DebuggableScheduledThreadPoolExecutor;
 import org.apache.cassandra.concurrent.JMXEnabledThreadPoolExecutor;
 import org.apache.cassandra.concurrent.Stage;
@@ -63,13 +61,8 @@ import org.apache.cassandra.net.RequestCallback;
 import org.apache.cassandra.net.Message;
 import org.apache.cassandra.net.MessagingService;
 import org.apache.cassandra.service.StorageService;
-import org.apache.cassandra.utils.CassandraVersion;
-import org.apache.cassandra.utils.ExecutorUtils;
 import org.apache.cassandra.utils.FBUtilities;
 import org.apache.cassandra.utils.JVMStabilityInspector;
-import org.apache.cassandra.utils.MBeanWrapper;
-import org.apache.cassandra.utils.NoSpamLogger;
-import org.apache.cassandra.utils.Pair;
 import org.apache.cassandra.utils.RecomputingSupplier;
 
 import static org.apache.cassandra.config.CassandraRelevantProperties.GOSSIPER_QUARANTINE_DELAY;
@@ -293,7 +286,7 @@ public class Gossiper implements IFailureDetectionEventListener, GossiperMBean
                 if (logger.isTraceEnabled())
                     logger.trace("My heartbeat is now {}", endpointStateMap.get(FBUtilities.getBroadcastAddressAndPort()).getHeartBeatState().getHeartBeatVersion());
                 final List<GossipDigest> gDigests = new ArrayList<>();
-                Gossiper.instance.makeRandomGossipDigest(gDigests);
+                Gossiper.instance.makeGossipDigest(gDigests);
 
                 if (gDigests.size() > 0)
                 {
@@ -699,29 +692,29 @@ public class Gossiper implements IFailureDetectionEventListener, GossiperMBean
     }
 
     /**
-     * The gossip digest is built based on randomization
-     * rather than just looping through the collection of live endpoints.
-     *
-     * @param gDigests list of Gossip Digests.
+     * @param gDigests list of Gossip Digests to be filled
      */
-    private void makeRandomGossipDigest(List<GossipDigest> gDigests)
+    private void makeGossipDigest(List<GossipDigest> gDigests)
     {
         EndpointState epState;
-        int generation = 0;
-        int maxVersion = 0;
+        int generation;
+        int maxVersion;
 
         // local epstate will be part of endpointStateMap
-        List<InetAddressAndPort> endpoints = new ArrayList<>(endpointStateMap.keySet());
-        Collections.shuffle(endpoints, random);
-        for (InetAddressAndPort endpoint : endpoints)
+        for (Entry<InetAddressAndPort, EndpointState> entry : endpointStateMap.entrySet())
         {
-            epState = endpointStateMap.get(endpoint);
+            epState = entry.getValue();
             if (epState != null)
             {
                 generation = epState.getHeartBeatState().getGeneration();
                 maxVersion = getMaxEndpointStateVersion(epState);
             }
-            gDigests.add(new GossipDigest(endpoint, generation, maxVersion));
+            else
+            {
+                generation = 0;
+                maxVersion = 0;
+            }
+            gDigests.add(new GossipDigest(entry.getKey(), generation, maxVersion));
         }
 
         if (logger.isTraceEnabled())