SERVER-59858 Add observability for tasks scheduled on reactor threads

1 files changed, 80 insertions, 0 deletions

diff --git a/src/mongo/util/executor_stats.h b/src/mongo/util/executor_stats.h
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+++ b/src/mongo/util/executor_stats.h
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+/**
+ *    Copyright (C) 2021-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the Server Side Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#pragma once
+
+#include "mongo/base/counter.h"
+#include "mongo/bson/bsonobjbuilder.h"
+#include "mongo/util/clock_source.h"
+#include "mongo/util/duration.h"
+#include "mongo/util/out_of_line_executor.h"
+
+namespace mongo {
+
+/**
+ * A utility to collect stats for tasks scheduled on an executor (e.g., the reactor thread).
+ *
+ * This class expects a clock source to measure the waiting and execution time of tasks. The clock
+ * source must always outlive instances of this class.
+ *
+ * This class collects stats for any task that is wrapped using `wrapTask`. The wrapped task may
+ * never outlive the instance of `ExecutorStats`.
+ *
+ * All public interfaces for this class are thread-safe.
+ */
+class ExecutorStats {
+public:
+    explicit ExecutorStats(ClockSource* clkSource) : _clkSource(clkSource) {}
+
+    using Task = OutOfLineExecutor::Task;
+    Task wrapTask(Task&&);
+
+    void serialize(BSONObjBuilder* bob) const;
+
+    static constexpr auto kNumBuckets = 22;
+
+private:
+    Counter64 _scheduled;
+    Counter64 _executed;
+
+    /**
+     * The following maintain histograms for tasks scheduled on the executor:
+     * `_waitingBuckets` represents the waiting time for the tasks pending execution.
+     * `_runningBuckets` keeps track of execution time of individual tasks after completion.
+     * Buckets 0 represents any recorded latency less than 1 milliseconds.
+     * Buckets 1 to 20 represent the 1-999 ms range.
+     * The last bucket represents any recorded latency that exceeds one second.
+     */
+    Counter64 _waitingBuckets[kNumBuckets];
+    Counter64 _runningBuckets[kNumBuckets];
+
+    ClockSource* const _clkSource;
+};
+
+}  // namespace mongo