From a3941d555542f3ddd68e933b9f99015425b4be01 Mon Sep 17 00:00:00 2001
From: Brandon Williams <brandonwilliams@apache.org>
Date: Tue, 21 Oct 2025 10:34:30 -0500
Subject: [PATCH] CNDB-15759: add
 unified_compaction.scaling_parameter_persistence flag

---
 .../db/compaction/unified/Controller.java     | 14 +++++++
 .../db/compaction/unified/ControllerTest.java | 37 +++++++++++++++++++
 2 files changed, 51 insertions(+)

diff --git a/src/java/org/apache/cassandra/db/compaction/unified/Controller.java b/src/java/org/apache/cassandra/db/compaction/unified/Controller.java
index cf59f410c15f..af0a596604a3 100644
--- a/src/java/org/apache/cassandra/db/compaction/unified/Controller.java
+++ b/src/java/org/apache/cassandra/db/compaction/unified/Controller.java
@@ -264,6 +264,14 @@ public abstract class Controller
     static final boolean ALLOW_UNSAFE_AGGRESSIVE_SSTABLE_EXPIRATION = Boolean.parseBoolean(System.getProperty(ALLOW_UNSAFE_AGGRESSIVE_SSTABLE_EXPIRATION_PROPERTY));
     static final boolean DEFAULT_ALLOW_UNSAFE_AGGRESSIVE_SSTABLE_EXPIRATION = false;
 
+    /**
+     * System property to control writing scaling parameters to JSON configuration file.
+     * When set to true (default), the controller will persist scaling parameters and flush size to disk.
+     * When set to false, persistence is disabled.
+     */
+    public static final String SCALING_PARAMETER_PERSISTENCE_PROPERTY = PREFIX + "scaling_parameter_persistence";
+    public static final boolean SCALING_PARAMETER_PERSISTENCE = Boolean.parseBoolean(System.getProperty(SCALING_PARAMETER_PERSISTENCE_PROPERTY, "true"));
+
     /**
      * This property allows seperate defaults for vector and non-vector tables.  If this property is set to true
      * and the table has a {@link VectorType}, the "vector" defaults are used over the regular defaults.  For instance,
@@ -439,6 +447,12 @@ public static File getControllerConfigPath(TableMetadata metadata)
 
     public static void storeOptions(TableMetadata metadata, int[] scalingParameters, long flushSizeBytes)
     {
+        if (!SCALING_PARAMETER_PERSISTENCE)
+        {
+            logger.debug("Scaling parameter persistence is disabled via {}. Skipping write to disk.", SCALING_PARAMETER_PERSISTENCE_PROPERTY);
+            return;
+        }
+
         if (SchemaConstants.isSystemKeyspace(metadata.keyspace))
             return;
         File f = getControllerConfigPath(metadata);
diff --git a/test/unit/org/apache/cassandra/db/compaction/unified/ControllerTest.java b/test/unit/org/apache/cassandra/db/compaction/unified/ControllerTest.java
index 84c7c57627b4..5120e89b1d7b 100644
--- a/test/unit/org/apache/cassandra/db/compaction/unified/ControllerTest.java
+++ b/test/unit/org/apache/cassandra/db/compaction/unified/ControllerTest.java
@@ -914,4 +914,41 @@ public void testGetLargestFactorizedShardCount()
         assertEquals(1, controller.getLargestFactorizedShardCount(-1.0));
         assertEquals(1, controller.getLargestFactorizedShardCount(-100.0));
     }
+
+    @Test
+    public void testScalingParameterPersistenceEnabled()
+    {
+        // Verify that by default (SCALING_PARAMETER_PERSISTENCE = true), storeOptions creates a file
+        assertTrue("Scaling parameter persistence should be enabled by default", Controller.SCALING_PARAMETER_PERSISTENCE);
+
+        TableMetadata testMetadata = standardCFMD("test_ks", "test_table").build();
+        int[] scalingParameters = new int[] { 0, 2, 4 };
+        long flushSize = 100 << 20; // 100 MB
+
+        // Store the options - should create a file when persistence is enabled
+        Controller.storeOptions(testMetadata, scalingParameters, flushSize);
+
+        // Verify the file was created
+        org.apache.cassandra.io.util.File configPath = Controller.getControllerConfigPath(testMetadata);
+        assertTrue("Config file should exist when persistence is enabled", configPath.exists());
+
+        // Clean up
+        configPath.delete();
+    }
+
+    @Test
+    public void testScalingParameterPersistenceSystemKeyspace()
+    {
+        // Verify that system keyspaces never write config files regardless of persistence setting
+        TableMetadata systemMetadata = standardCFMD("system", "test_table").build();
+        int[] scalingParameters = new int[] { 0, 2, 4 };
+        long flushSize = 100 << 20; // 100 MB
+
+        // Store the options - should not create a file for system keyspace
+        Controller.storeOptions(systemMetadata, scalingParameters, flushSize);
+
+        // Verify the file was NOT created
+        org.apache.cassandra.io.util.File configPath = Controller.getControllerConfigPath(systemMetadata);
+        assertFalse("Config file should not exist for system keyspace", configPath.exists());
+    }
 }