Fix WAL throttle threshold fallback on hot reload

iotdb-core/datanode/src/main/java/org/apache/iotdb/db/conf/IoTDBDescriptor.java

@@ -1798,6 +1798,11 @@ private void loadWALHotModifiedProps(TrimProperties properties) throws IOExcepti
     }
 
     long throttleDownThresholdInByte = Long.parseLong(getWalThrottleThreshold(properties));
+    if (throttleDownThresholdInByte < 0) {
+      throttleDownThresholdInByte =
+          Long.parseLong(
+              ConfigurationFileUtils.getConfigurationDefaultValue(DEFAULT_WAL_THRESHOLD_NAME[1]));
+    }
     if (throttleDownThresholdInByte > 0) {
       conf.setThrottleThreshold(throttleDownThresholdInByte);
     }
@@ -2401,6 +2406,8 @@ private void overlayEffectiveConfigurationValues() {
         Long.toString(commonDescriptor.getConfig().getSortBufferSize()));
     ConfigurationFileUtils.updateAppliedProperties(
         "mods_cache_size_limit_per_fi_in_bytes", Long.toString(conf.getModsCacheSizeLimitPerFI()));
+    ConfigurationFileUtils.updateAppliedProperties(
+        DEFAULT_WAL_THRESHOLD_NAME[1], Long.toString(conf.getThrottleThreshold()));
   }
 
   private void loadQuerySampleThroughput(TrimProperties properties) throws IOException {

iotdb-core/datanode/src/test/java/org/apache/iotdb/db/conf/PropertiesTest.java

@@ -19,6 +19,7 @@
 
 package org.apache.iotdb.db.conf;
 
+import org.apache.iotdb.commons.conf.ConfigurationFileUtils;
 import org.apache.iotdb.commons.conf.TrimProperties;
 import org.apache.iotdb.commons.utils.RegionMigrationFileRemoveRateLimiter;
 
@@ -36,6 +37,33 @@
 import static com.tngtech.archunit.lang.syntax.ArchRuleDefinition.noClasses;
 
 public class PropertiesTest {
+  @Test
+  public void testHotReloadNegativeWalThrottleThresholdUsesDefault() throws Exception {
+    final String key = "wal_throttle_threshold_in_byte";
+    final long configuredThreshold = 1024 * 1024 * 1024L;
+    final long defaultThreshold =
+        Long.parseLong(ConfigurationFileUtils.getConfigurationDefaultValue(key));
+    final IoTDBDescriptor descriptor = IoTDBDescriptor.getInstance();
+    final long originalThreshold = descriptor.getConfig().getThrottleThreshold();
+
+    try {
+      final TrimProperties properties = new TrimProperties();
+      properties.setProperty(key, Long.toString(configuredThreshold));
+      descriptor.loadHotModifiedProps(properties);
+      Assert.assertEquals(configuredThreshold, descriptor.getConfig().getThrottleThreshold());
+
+      properties.setProperty(key, "-1");
+      descriptor.loadHotModifiedProps(properties);
+      Assert.assertEquals(defaultThreshold, descriptor.getConfig().getThrottleThreshold());
+      Assert.assertEquals(
+          Long.toString(defaultThreshold), ConfigurationFileUtils.getAppliedProperties().get(key));
+    } finally {
+      final TrimProperties properties = new TrimProperties();
+      properties.setProperty(key, Long.toString(originalThreshold));
+      descriptor.loadHotModifiedProps(properties);
+    }
+  }
+
   @Test
   public void testHotReloadRegionMigrationFileRemoveSpeedLimit() throws Exception {
     IoTDBDescriptor descriptor = IoTDBDescriptor.getInstance();