From 70626d685e0f8a4b09ac8b36ef9aa0a4a8f43c0d Mon Sep 17 00:00:00 2001
From: ssekaran <s_sekaran@apple.com>
Date: Mon, 16 Feb 2026 13:11:05 -0800
Subject: [PATCH] CASSANDRA-21177- Adding option for randomizing memtable type
 in Simulator tests

---
 .../simulator/ClusterSimulation.java          | 26 +++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/test/simulator/main/org/apache/cassandra/simulator/ClusterSimulation.java b/test/simulator/main/org/apache/cassandra/simulator/ClusterSimulation.java
index f7f934638553..dae0ddfe6d81 100644
--- a/test/simulator/main/org/apache/cassandra/simulator/ClusterSimulation.java
+++ b/test/simulator/main/org/apache/cassandra/simulator/ClusterSimulation.java
@@ -38,6 +38,9 @@
 import com.google.common.util.concurrent.AsyncFunction;
 import com.google.common.util.concurrent.FutureCallback;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 import org.apache.cassandra.concurrent.ExecutorFactory;
 import org.apache.cassandra.config.ParameterizedClass;
 import org.apache.cassandra.distributed.Cluster;
@@ -112,6 +115,8 @@
 @SuppressWarnings("RedundantCast")
 public class ClusterSimulation<S extends Simulation> implements AutoCloseable
 {
+    private static final Logger logger = LoggerFactory.getLogger(ClusterSimulation.class);
+
     public static final Class<?>[] SHARE = new Class[]
                                         {
                                             AsyncFunction.class,
@@ -188,6 +193,7 @@ public static abstract class Builder<S extends Simulation>
         protected HeapPool.Logged.Listener memoryListener;
         protected SimulatedTime.Listener timeListener = (i1, i2) -> {};
         protected LongConsumer onThreadLocalRandomCheck;
+        protected Boolean useTrieMemtable = null;  // null = random
 
         public Debug debug()
         {
@@ -516,6 +522,12 @@ public Builder<S> onThreadLocalRandomCheck(LongConsumer runnable)
             return this;
         }
 
+        public Builder<S> useTrieMemtable(boolean useTrie)
+        {
+            this.useTrieMemtable = useTrie;
+            return this;
+        }
+
         public abstract ClusterSimulation<S> create(long seed) throws IOException;
     }
 
@@ -654,6 +666,12 @@ public ClusterSimulation(RandomSource random, long seed, int uniqueNum,
 
         execution = new SimulatedExecution();
 
+        boolean useTrieMemtable = builder.useTrieMemtable != null
+                                  ? builder.useTrieMemtable
+                                  : random.uniform(0, 2) == 0; // 50/50 chance
+        logger.info("Seed 0x{} using memtable: {}", Long.toHexString(seed),
+                    useTrieMemtable ? "TrieMemtable" : "SkipListMemtable");
+
         KindOfSequence kindOfDriftSequence = Choices.uniform(KindOfSequence.values()).choose(random);
         KindOfSequence kindOfDiscontinuitySequence = Choices.uniform(KindOfSequence.values()).choose(random);
         time = new SimulatedTime(numOfNodes, random, 1577836800000L /*Jan 1st UTC*/, builder.clockDriftNanos, kindOfDriftSequence,
@@ -700,6 +718,14 @@ public ClusterSimulation(RandomSource random, long seed, int uniqueNum,
 
                              if (commitlogCompressed)
                                  config.set("commitlog_compression", new ParameterizedClass(LZ4Compressor.class.getName(), emptyMap()));
+
+                             if (useTrieMemtable)
+                             {
+                                 config.set("memtable", Map.of(
+                                           "configurations", Map.of(
+                                               "default", Map.of("class_name", "TrieMemtable"))));
+                             }
+
                              configUpdater.accept(threadAllocator.update(config));
                          })
                          .withInstanceInitializer(new IInstanceInitializer()