Allow configuring driver threads based on the number of cores

Inspired by trinodb/trino#20772

presto-docs/src/main/sphinx/admin/properties.rst

@@ -546,6 +546,12 @@ in performance due to a context switching. The number of active threads is avail
 via the ``RunningSplits`` property of the
 ``com.facebook.presto.execution.executor:name=TaskExecutor.RunningSplits`` JXM object.
 
+The number of threads can be configured using either an absolute value (for example, ``10``)
+or a value relative to the number of available CPU cores (for example, ``1.5C``). When
+using a relative value, the number of threads is calculated based on the available CPU
+cores multiplied by the specified factor (for example, ``1.5``) and rounded to the
+nearest integer.
+
 ``task.min-drivers``
 ^^^^^^^^^^^^^^^^^^^^
 

presto-main/src/main/java/com/facebook/presto/execution/TaskManagerConfig.java

@@ -281,9 +281,9 @@ public int getMaxWorkerThreads()
 
     @LegacyConfig("task.shard.max-threads")
     @Config("task.max-worker-threads")
-    public TaskManagerConfig setMaxWorkerThreads(int maxWorkerThreads)
+    public TaskManagerConfig setMaxWorkerThreads(String maxWorkerThreads)
     {
-        this.maxWorkerThreads = maxWorkerThreads;
+        this.maxWorkerThreads = ThreadCountParser.parse(maxWorkerThreads);
         return this;
     }
 

presto-main/src/main/java/com/facebook/presto/execution/ThreadCountParser.java

@@ -0,0 +1,53 @@
+/*
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.facebook.presto.execution;
+
+import com.google.common.annotations.VisibleForTesting;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static java.lang.Double.parseDouble;
+import static java.lang.Integer.parseInt;
+import static java.lang.Math.max;
+import static java.lang.Math.round;
+import static java.lang.Math.toIntExact;
+
+public class ThreadCountParser
+{
+    private static final String PER_CORE_SUFFIX = "C";
+
+    private ThreadCountParser() {}
+
+    public static int parse(String value)
+    {
+        return parse(value, Runtime.getRuntime().availableProcessors());
+    }
+
+    @VisibleForTesting
+    static int parse(String value, int availableProcessors)
+    {
+        int threads;
+        if (value.endsWith(PER_CORE_SUFFIX)) {
+            double multiplier = parseDouble(value.substring(0, value.length() - PER_CORE_SUFFIX.length()).trim());
+            checkArgument(multiplier > 0, "Thread multiplier must be positive: %s", multiplier);
+            threads = toIntExact(round(multiplier * availableProcessors));
+            threads = max(threads, 1);
+        }
+        else {
+            threads = parseInt(value);
+        }
+
+        checkArgument(threads > 0, "Thread count must be positive: %s", threads);
+        return threads;
+    }
+}

presto-main/src/test/java/com/facebook/presto/execution/TestTaskManagerConfig.java

@@ -46,7 +46,7 @@ public void testDefaults()
                 .setTaskCpuTimerEnabled(true)
                 .setPerOperatorAllocationTrackingEnabled(false)
                 .setTaskAllocationTrackingEnabled(false)
-                .setMaxWorkerThreads(Runtime.getRuntime().availableProcessors() * 2)
+                .setMaxWorkerThreads("2C")
                 .setMinDrivers(Runtime.getRuntime().availableProcessors() * 2 * 2)
                 .setMinDriversPerTask(3)
                 .setMaxDriversPerTask(Integer.MAX_VALUE)
@@ -141,7 +141,7 @@ public void testExplicitPropertyMappings()
                 .setShareIndexLoading(true)
                 .setMaxPartialAggregationMemoryUsage(new DataSize(32, Unit.MEGABYTE))
                 .setMaxLocalExchangeBufferSize(new DataSize(33, Unit.MEGABYTE))
-                .setMaxWorkerThreads(3)
+                .setMaxWorkerThreads("3")
                 .setMinDrivers(2)
                 .setMinDriversPerTask(5)
                 .setMaxDriversPerTask(13)

presto-main/src/test/java/com/facebook/presto/execution/TestThreadCountParser.java

@@ -0,0 +1,49 @@
+/*
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.facebook.presto.execution;
+
+import org.testng.annotations.Test;
+
+import static com.facebook.presto.execution.ThreadCountParser.parse;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+import static org.testng.Assert.assertEquals;
+
+public class TestThreadCountParser
+{
+    @Test
+    public void testParse()
+    {
+        assertEquals(parse("1"), 1);
+        assertEquals(parse("100"), 100);
+        assertEquals(parse("1", 1), 1);
+        assertEquals(parse("1", 2), 1);
+        assertEquals(parse("100", 4), 100);
+        assertEquals(parse("1C", 4), 4);
+        assertEquals(parse("2C", 8), 16);
+        assertEquals(parse("1.5C", 6), 9);
+        assertEquals(parse("0.1C", 1), 1);
+        assertThatThrownBy(() -> parse("0"))
+                .hasMessageContaining("Thread count must be positive");
+        assertThatThrownBy(() -> parse("-1"))
+                .hasMessageContaining("Thread count must be positive");
+        assertThatThrownBy(() -> parse("0C"))
+                .hasMessageContaining("Thread multiplier must be positive");
+        assertThatThrownBy(() -> parse("-1C"))
+                .hasMessageContaining("Thread multiplier must be positive");
+        assertThatThrownBy(() -> parse("abc"))
+                .isInstanceOf(NumberFormatException.class);
+        assertThatThrownBy(() -> parse("abcC"))
+                .isInstanceOf(NumberFormatException.class);
+    }
+}