From e936b2cc1ba7f525c636de5f9fb1780ca70f1762 Mon Sep 17 00:00:00 2001
From: Jordan West <jordanw@netflix.com>
Date: Mon, 9 Jan 2023 12:04:50 -0800
Subject: [PATCH] fix serialization error in getsstables --show-levels

Patch by Jordan West; Reviewed by Brandon Williams, Cheng Wang for CASSANDRA-18140;
---
 CHANGES.txt                                   |  1 +
 .../cassandra/db/ColumnFamilyStore.java       | 19 +++++++++++++------
 .../cassandra/db/ColumnFamilyStoreMBean.java  |  2 +-
 .../org/apache/cassandra/tools/NodeProbe.java |  3 +--
 .../cassandra/tools/nodetool/GetSSTables.java |  4 ++--
 5 files changed, 18 insertions(+), 11 deletions(-)

diff --git a/CHANGES.txt b/CHANGES.txt
index 6ffdfb89aae1..682316e39731 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -1,4 +1,5 @@
 4.2
+ * Fix serialization error in new getsstables --show-levels option (CASSANDRA-18140)
  * Use checked casts when reading vints as ints (CASSANDRA-18099)
  * Add Mutation Serialization Caching (CASSANDRA-17998)
  * Only reload compaction strategies if disk boundaries change (CASSANDRA-17874)
diff --git a/src/java/org/apache/cassandra/db/ColumnFamilyStore.java b/src/java/org/apache/cassandra/db/ColumnFamilyStore.java
index b00a77ab408c..d656c373804d 100644
--- a/src/java/org/apache/cassandra/db/ColumnFamilyStore.java
+++ b/src/java/org/apache/cassandra/db/ColumnFamilyStore.java
@@ -64,12 +64,10 @@
 import com.google.common.base.Predicates;
 import com.google.common.base.Strings;
 import com.google.common.base.Throwables;
-import com.google.common.collect.HashMultimap;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.Iterables;
 import com.google.common.collect.Lists;
-import com.google.common.collect.Multimap;
 import com.google.common.collect.Sets;
 import com.google.common.util.concurrent.RateLimiter;
 import org.slf4j.Logger;
@@ -1946,14 +1944,23 @@ public List<String> getSSTablesForKey(String key, boolean hexFormat)
         return withSSTablesForKey(key, hexFormat, SSTableReader::getFilename);
     }
 
-    public Map<Integer, Collection<String>> getSSTablesForKeyWithLevel(String key, boolean hexFormat)
+    public Map<Integer, Set<String>> getSSTablesForKeyWithLevel(String key, boolean hexFormat)
     {
         List<Pair<Integer, String>> ssts = withSSTablesForKey(key, hexFormat, sstr -> Pair.create(sstr.getSSTableLevel(), sstr.getFilename()));
-        Multimap<Integer, String> result = HashMultimap.create();
+        HashMap<Integer, Set<String>> result = new HashMap<>();
         for (Pair<Integer, String> sst : ssts)
-            result.put(sst.left, sst.right);
+        {
+            Set<String> perLevel = result.get(sst.left);
+            if (perLevel == null)
+            {
+                perLevel = new HashSet<>();
+                result.put(sst.left, perLevel);
+            }
 
-        return result.asMap();
+            perLevel.add(sst.right);
+        }
+
+        return result;
     }
 
     public <T> List<T> withSSTablesForKey(String key, boolean hexFormat, Function<SSTableReader, T> mapper)
diff --git a/src/java/org/apache/cassandra/db/ColumnFamilyStoreMBean.java b/src/java/org/apache/cassandra/db/ColumnFamilyStoreMBean.java
index 629f431547df..1a90875c4f50 100644
--- a/src/java/org/apache/cassandra/db/ColumnFamilyStoreMBean.java
+++ b/src/java/org/apache/cassandra/db/ColumnFamilyStoreMBean.java
@@ -168,7 +168,7 @@ public interface ColumnFamilyStoreMBean
      * @param hexFormat
      * @return list of filenames and levels containing the key
      */
-    public Map<Integer, Collection<String>> getSSTablesForKeyWithLevel(String key, boolean hexFormat);
+    public Map<Integer, Set<String>> getSSTablesForKeyWithLevel(String key, boolean hexFormat);
 
     /**
      * Load new sstables from the given directory
diff --git a/src/java/org/apache/cassandra/tools/NodeProbe.java b/src/java/org/apache/cassandra/tools/NodeProbe.java
index 687ab0a0ab51..9217ff36c6ae 100644
--- a/src/java/org/apache/cassandra/tools/NodeProbe.java
+++ b/src/java/org/apache/cassandra/tools/NodeProbe.java
@@ -30,7 +30,6 @@
 import java.rmi.server.RMISocketFactory;
 import java.util.AbstractMap;
 import java.util.ArrayList;
-import java.util.Collection;
 import java.util.Collections;
 import java.util.Comparator;
 import java.util.HashMap;
@@ -1045,7 +1044,7 @@ public List<String> getSSTables(String keyspace, String cf, String key, boolean
         return cfsProxy.getSSTablesForKey(key, hexFormat);
     }
 
-    public Map<Integer, Collection<String>> getSSTablesWithLevel(String keyspace, String cf, String key, boolean hexFormat)
+    public Map<Integer, Set<String>> getSSTablesWithLevel(String keyspace, String cf, String key, boolean hexFormat)
     {
         ColumnFamilyStoreMBean cfsProxy = getCfsProxy(keyspace, cf);
         return cfsProxy.getSSTablesForKeyWithLevel(key, hexFormat);
diff --git a/src/java/org/apache/cassandra/tools/nodetool/GetSSTables.java b/src/java/org/apache/cassandra/tools/nodetool/GetSSTables.java
index e321e31f2009..657e0ec61990 100644
--- a/src/java/org/apache/cassandra/tools/nodetool/GetSSTables.java
+++ b/src/java/org/apache/cassandra/tools/nodetool/GetSSTables.java
@@ -22,9 +22,9 @@
 import io.airlift.airline.Command;
 
 import java.util.ArrayList;
-import java.util.Collection;
 import java.util.List;
 import java.util.Map;
+import java.util.Set;
 
 import io.airlift.airline.Option;
 import org.apache.cassandra.tools.NodeProbe;
@@ -54,7 +54,7 @@ public void execute(NodeProbe probe)
 
         if (showLevels && probe.isLeveledCompaction(ks, cf))
         {
-            Map<Integer, Collection<String>> sstables = probe.getSSTablesWithLevel(ks, cf, key, hexFormat);
+            Map<Integer, Set<String>> sstables = probe.getSSTablesWithLevel(ks, cf, key, hexFormat);
             for (Integer level : sstables.keySet())
                 for (String sstable : sstables.get(level))
                     probe.output().out.println(level + ": " + sstable);