From 0040482e269d77165f664e71b0c7c487f3917cb2 Mon Sep 17 00:00:00 2001
From: Dmitry Konstantinov <netudima@gmail.com>
Date: Thu, 23 Jul 2026 03:15:55 +0100
Subject: [PATCH] Reduce disk space usage by CommitLogSegmentManagerCDCTest

patch by Dmitry Konstantinov; reviewed by Michael Semb Wever for CASSANDRA-21534
---
 .../CommitLogSegmentManagerCDCTest.java       | 35 +++++++++++++++++--
 1 file changed, 32 insertions(+), 3 deletions(-)

diff --git a/test/unit/org/apache/cassandra/db/commitlog/CommitLogSegmentManagerCDCTest.java b/test/unit/org/apache/cassandra/db/commitlog/CommitLogSegmentManagerCDCTest.java
index 6f56089259..59a3a46e54 100644
--- a/test/unit/org/apache/cassandra/db/commitlog/CommitLogSegmentManagerCDCTest.java
+++ b/test/unit/org/apache/cassandra/db/commitlog/CommitLogSegmentManagerCDCTest.java
@@ -30,6 +30,7 @@ import java.util.concurrent.TimeUnit;
 
 import com.google.common.util.concurrent.Uninterruptibles;
 
+import org.junit.After;
 import org.junit.Assert;
 import org.junit.Before;
 import org.junit.BeforeClass;
@@ -42,9 +43,11 @@ import org.apache.cassandra.db.ColumnFamilyStore;
 import org.apache.cassandra.db.Keyspace;
 import org.apache.cassandra.db.RowUpdateBuilder;
 import org.apache.cassandra.db.commitlog.CommitLogSegment.CDCState;
+import org.apache.cassandra.db.lifecycle.LifecycleTransaction;
 import org.apache.cassandra.exceptions.CDCWriteException;
 import org.apache.cassandra.io.util.File;
 import org.apache.cassandra.io.util.FileReader;
+import org.apache.cassandra.schema.Schema;
 import org.apache.cassandra.schema.TableMetadata;
 
 public class CommitLogSegmentManagerCDCTest extends CQLTester
@@ -57,7 +60,11 @@ public class CommitLogSegmentManagerCDCTest extends CQLTester
     {
         ServerTestUtils.daemonInitialization();
         DatabaseDescriptor.setCDCEnabled(true);
-        DatabaseDescriptor.setCDCTotalSpaceInMiB(1024);
+        // The bulk writes are sized to commitLogSegmentSize/3, so the suite's disk footprint scales
+        // with the segment size; shrink it to the 1 MiB floor. Cap the default CDC space too: bulkWrite
+        // writes ~2x the CDC limit, so this bounds how much the non-blocking cases flush to disk.
+        DatabaseDescriptor.setCommitLogSegmentSize(1);
+        DatabaseDescriptor.setCDCTotalSpaceInMiB(100);
         CQLTester.setUpClass();
     }
 
@@ -71,6 +78,24 @@ public class CommitLogSegmentManagerCDCTest extends CQLTester
         ((CommitLogSegmentManagerCDC)CommitLog.instance.segmentManager).updateCDCTotalSize();
     }
 
+    @After
+    public void afterTest() throws Throwable
+    {
+        // Reclaim the SSTables this test wrote so data/ doesn't grow across methods; CQLTester#afterTest
+        // only clears schema-tracking state. Do NOT stop/delete the commit log here: super.afterTest()
+        // resets the CMS, whose schema re-application runs asynchronously on the TCM log follower, and
+        // deleting segments underneath it makes CDC hard-linking fail ("hard link to file that does not
+        // exist"). beforeTest() restarts the commit log for the next test instead.
+        Keyspace ks = Schema.instance.getKeyspaceInstance(keyspace());
+        if (ks != null)
+        {
+            for (ColumnFamilyStore cfs : ks.getColumnFamilyStores())
+                cfs.truncateBlockingWithoutSnapshot();
+            LifecycleTransaction.waitForDeletions();
+        }
+        super.afterTest();
+    }
+
     @Test
     public void testCDCWriteFailure() throws Throwable
     {
@@ -456,10 +481,14 @@ public class CommitLogSegmentManagerCDCTest extends CQLTester
     {
         TableMetadata ccfm = Keyspace.open(keyspace()).getColumnFamilyStore(tableName).metadata();
         boolean blockWrites = DatabaseDescriptor.getCDCBlockWrites();
-        // Spin to make sure we hit CDC capacity
+        // Write enough to overflow the configured CDC limit so we reliably hit capacity. Derive the
+        // count from the CDC size and mutation size. Blocking mode stops
+        // early on the first CDCWriteException; non-blocking mode writes the whole run, recycling
+        // older segments (2x the fill count keeps it exercising recycling without over-writing).
+        int writes = 2 * (int) (DatabaseDescriptor.getCDCTotalSpace() / mutationSize);
         try
         {
-            for (int i = 0; i < 1000; i++)
+            for (int i = 0; i < writes; i++)
             {
                 new RowUpdateBuilder(ccfm, 0, i)
                 .add("data", randomizeBuffer(mutationSize))