Reduce allocations in DefaultQueryOptions when read thresholds are enabled

patch by Francisco Guerrero; reviewed by Dmitry Konstantinov, Stefan Miklosovic for CASSANDRA-21467

CHANGES.txt

@@ -1,4 +1,5 @@
 6.0-alpha2
+ * Reduce allocations in DefaultQueryOptions (CASSANDRA-21467)
  * Coordinator load-shedding returns OverloadedException without setting streamId, misrouting query responses (CASSANDRA-21508)
  * Reduce number of scheduledTasks on metric id release in ThreadLocalMetrics (CASSANDRA-21475)
  * Cache various Enum.values() used in deserialization to avoid per-read array allocation (CASSANDRA-21528)

src/java/org/apache/cassandra/config/DatabaseDescriptor.java

@@ -85,6 +85,7 @@ import org.apache.cassandra.config.Config.DiskAccessMode;
 import org.apache.cassandra.config.Config.PaxosOnLinearizabilityViolation;
 import org.apache.cassandra.config.Config.PaxosStatePurging;
 import org.apache.cassandra.config.DurationSpec.IntMillisecondsBound;
+import org.apache.cassandra.cql3.QueryOptions;
 import org.apache.cassandra.db.ConsistencyLevel;
 import org.apache.cassandra.db.commitlog.AbstractCommitLogSegmentManager;
 import org.apache.cassandra.db.commitlog.CommitLog;
@@ -272,6 +273,8 @@ public class DatabaseDescriptor
 
     public static volatile boolean allowUnlimitedConcurrentValidations = ALLOW_UNLIMITED_CONCURRENT_VALIDATIONS.getBoolean();
 
+    private static volatile QueryOptions.DefaultReadThresholds defaultReadThresholds;
+
     /**
      * RetryStrategy which provides exponential backoff with full jitter, for use by both CMS and non-CMS members
      * when submitting a Commit request. The range and increments of the backoff times are defined by
@@ -5555,6 +5558,14 @@ public class DatabaseDescriptor
         return conf.invalid_legacy_protocol_magic_no_spam_enabled;
     }
 
+    public static QueryOptions.DefaultReadThresholds getDefaultReadThresholds()
+    {
+        if (defaultReadThresholds == null)
+            defaultReadThresholds = new QueryOptions.DefaultReadThresholds(getCoordinatorReadSizeWarnThreshold(),
+                                                                           getCoordinatorReadSizeFailThreshold());
+        return defaultReadThresholds;
+    }
+
     public static boolean getReadThresholdsEnabled()
     {
         return conf.read_thresholds_enabled;
@@ -5579,6 +5590,7 @@ public class DatabaseDescriptor
     {
         logger.info("updating  coordinator_read_size_warn_threshold to {}", value);
         conf.coordinator_read_size_warn_threshold = value;
+        defaultReadThresholds = new QueryOptions.DefaultReadThresholds(value, getCoordinatorReadSizeFailThreshold());
     }
 
     @Nullable
@@ -5591,6 +5603,7 @@ public class DatabaseDescriptor
     {
         logger.info("updating  coordinator_read_size_fail_threshold to {}", value);
         conf.coordinator_read_size_fail_threshold = value;
+        defaultReadThresholds = new QueryOptions.DefaultReadThresholds(getCoordinatorReadSizeWarnThreshold(), value);
     }
 
     @Nullable

src/java/org/apache/cassandra/cql3/QueryOptions.java

@@ -322,7 +322,7 @@ public abstract class QueryOptions implements RealTimeFunctionContext
             // if daemon initialization hasn't happened yet (very common in tests) then ignore
             if (!DatabaseDescriptor.isDaemonInitialized() || !DatabaseDescriptor.getReadThresholdsEnabled())
                 return DisabledReadThresholds.INSTANCE;
-            return new DefaultReadThresholds(DatabaseDescriptor.getCoordinatorReadSizeWarnThreshold(), DatabaseDescriptor.getCoordinatorReadSizeFailThreshold());
+            return DatabaseDescriptor.getDefaultReadThresholds();
         }
     }
 
@@ -349,7 +349,7 @@ public abstract class QueryOptions implements RealTimeFunctionContext
         }
     }
 
-    private static class DefaultReadThresholds implements ReadThresholds
+    public static class DefaultReadThresholds implements ReadThresholds
     {
         private final long warnThresholdBytes;
         private final long abortThresholdBytes;

test/unit/org/apache/cassandra/config/DatabaseDescriptorRefTest.java

@@ -123,6 +123,8 @@ public class DatabaseDescriptorRefTest
     "org.apache.cassandra.config.Config$CorruptedTombstoneStrategy",
     "org.apache.cassandra.config.Config$BatchlogEndpointStrategy",
     "org.apache.cassandra.config.Config$TombstonesMetricGranularity",
+    "org.apache.cassandra.cql3.QueryOptions$DefaultReadThresholds",
+    "org.apache.cassandra.cql3.QueryOptions$ReadThresholds",
     "org.apache.cassandra.service.consensus.UnsupportedTransactionConsistencyLevel",
     "org.apache.cassandra.repair.autorepair.AutoRepairConfig",
     "org.apache.cassandra.repair.autorepair.AutoRepairConfig$Options",