From e68897be05738ea7ddc091adc8cbec537ddfad4d Mon Sep 17 00:00:00 2001
From: nivy <nivy@apple.com>
Date: Wed, 29 Jul 2026 19:59:38 -0700
Subject: [PATCH] Allow setCompressedReadAheadBufferSizeInKb(0) to disable RAB

---
 .../cassandra/config/DatabaseDescriptor.java  |  4 ++--
 .../config/DatabaseDescriptorTest.java        | 24 +++++++++++++++++++
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/src/java/org/apache/cassandra/config/DatabaseDescriptor.java b/src/java/org/apache/cassandra/config/DatabaseDescriptor.java
index 0885b72d2f..cfe7c0ef68 100644
--- a/src/java/org/apache/cassandra/config/DatabaseDescriptor.java
+++ b/src/java/org/apache/cassandra/config/DatabaseDescriptor.java
@@ -3056,8 +3056,8 @@ public class DatabaseDescriptor
 
     public static void setCompressedReadAheadBufferSizeInKb(int sizeInKb)
     {
-        if (sizeInKb < 256)
-            throw new IllegalArgumentException("compressed_read_ahead_buffer_size_in_kb must be at least 256KiB");
+        if (sizeInKb < 0 || (sizeInKb > 0 && sizeInKb < 256))
+            throw new IllegalArgumentException("compressed_read_ahead_buffer_size_in_kb must be at least 256KiB (set to 0 to disable)");
 
         conf.compressed_read_ahead_buffer_size = createIntKibibyteBoundAndEnsureItIsValidForByteConversion(sizeInKb, "compressed_read_ahead_buffer_size");
     }
diff --git a/test/unit/org/apache/cassandra/config/DatabaseDescriptorTest.java b/test/unit/org/apache/cassandra/config/DatabaseDescriptorTest.java
index c54d727ea8..26dcb60588 100644
--- a/test/unit/org/apache/cassandra/config/DatabaseDescriptorTest.java
+++ b/test/unit/org/apache/cassandra/config/DatabaseDescriptorTest.java
@@ -1212,4 +1212,28 @@ public class DatabaseDescriptorTest
             conf.local_system_data_file_directory = savedLocalSystemDir;
         }
     }
+
+    @Test
+    public void testSetCompressedReadAheadBufferSizeInKb()
+    {
+        int original = DatabaseDescriptor.getCompressedReadAheadBufferSizeInKB();
+        try
+        {
+            // 0 should be a legal value, and represents disabling read-ahead buffer
+            DatabaseDescriptor.setCompressedReadAheadBufferSizeInKb(0);
+            assertEquals(0, DatabaseDescriptor.getCompressedReadAheadBufferSizeInKB());
+            assertEquals(0, DatabaseDescriptor.getCompressedReadAheadBufferSize());
+
+            Assertions.assertThatThrownBy(() -> DatabaseDescriptor.setCompressedReadAheadBufferSizeInKb(255))
+                      .isInstanceOf(IllegalArgumentException.class)
+                      .hasMessage("compressed_read_ahead_buffer_size_in_kb must be at least 256KiB (set to 0 to disable)");
+
+            DatabaseDescriptor.setCompressedReadAheadBufferSizeInKb(256);
+            assertEquals(256, DatabaseDescriptor.getCompressedReadAheadBufferSizeInKB());
+        }
+        finally
+        {
+            DatabaseDescriptor.setCompressedReadAheadBufferSizeInKb(original);
+        }
+    }
 }