Performance measurement APIs | Node.js v15.14.0 Documentation (original) (raw)

Source Code: lib/perf_hooks.js

This module provides an implementation of a subset of the W3CWeb Performance APIs as well as additional APIs for Node.js-specific performance measurements.

Node.js supports the following Web Performance APIs:

const { PerformanceObserver, performance } = require('perf_hooks');

const obs = new PerformanceObserver((items) => {
  console.log(items.getEntries()[0].duration);
  performance.clearMarks();
});
obs.observe({ entryTypes: ['measure'] });
performance.measure('Start to Now');

performance.mark('A');
doSomeLongRunningProcess(() => {
  performance.measure('A to Now', 'A');

  performance.mark('B');
  performance.measure('A to B', 'A', 'B');
});

perf_hooks.performance#

Added in: v8.5.0

An object that can be used to collect performance metrics from the current Node.js instance. It is similar to window.performance in browsers.

performance.clearMarks([name])#

Added in: v8.5.0

If name is not provided, removes all PerformanceMark objects from the Performance Timeline. If name is provided, removes only the named mark.

performance.eventLoopUtilization([utilization1[, utilization2]])#

Added in: v14.10.0, v12.19.0

The eventLoopUtilization() method returns an object that contains the cumulative duration of time the event loop has been both idle and active as a high resolution milliseconds timer. The utilization value is the calculated Event Loop Utilization (ELU).

If bootstrapping has not yet finished on the main thread the properties have the value of 0. The ELU is immediately available on Worker threads since bootstrap happens within the event loop.

Both utilization1 and utilization2 are optional parameters.

If utilization1 is passed, then the delta between the current call's activeand idle times, as well as the corresponding utilization value are calculated and returned (similar to process.hrtime()).

If utilization1 and utilization2 are both passed, then the delta is calculated between the two arguments. This is a convenience option because, unlike process.hrtime(), calculating the ELU is more complex than a single subtraction.

ELU is similar to CPU utilization, except that it only measures event loop statistics and not CPU usage. It represents the percentage of time the event loop has spent outside the event loop's event provider (e.g. epoll_wait). No other CPU idle time is taken into consideration. The following is an example of how a mostly idle process will have a high ELU.

'use strict';
const { eventLoopUtilization } = require('perf_hooks').performance;
const { spawnSync } = require('child_process');

setImmediate(() => {
  const elu = eventLoopUtilization();
  spawnSync('sleep', ['5']);
  console.log(eventLoopUtilization(elu).utilization);
});

Although the CPU is mostly idle while running this script, the value ofutilization is 1. This is because the call tochild_process.spawnSync() blocks the event loop from proceeding.

Passing in a user-defined object instead of the result of a previous call toeventLoopUtilization() will lead to undefined behavior. The return values are not guaranteed to reflect any correct state of the event loop.

performance.mark([name])#

Added in: v8.5.0

Creates a new PerformanceMark entry in the Performance Timeline. APerformanceMark is a subclass of PerformanceEntry whoseperformanceEntry.entryType is always 'mark', and whoseperformanceEntry.duration is always 0. Performance marks are used to mark specific significant moments in the Performance Timeline.

performance.measure(name[, startMark[, endMark]])#

Creates a new PerformanceMeasure entry in the Performance Timeline. APerformanceMeasure is a subclass of PerformanceEntry whoseperformanceEntry.entryType is always 'measure', and whoseperformanceEntry.duration measures the number of milliseconds elapsed sincestartMark and endMark.

The startMark argument may identify any existing PerformanceMark in the Performance Timeline, or may identify any of the timestamp properties provided by the PerformanceNodeTiming class. If the named startMark does not exist, then startMark is set to timeOrigin by default.

The optional endMark argument must identify any existing PerformanceMarkin the Performance Timeline or any of the timestamp properties provided by thePerformanceNodeTiming class. endMark will be performance.now()if no parameter is passed, otherwise if the named endMark does not exist, an error will be thrown.

performance.nodeTiming#

Added in: v8.5.0

This property is an extension by Node.js. It is not available in Web browsers.

An instance of the PerformanceNodeTiming class that provides performance metrics for specific Node.js operational milestones.

performance.now()#

Added in: v8.5.0

Returns the current high resolution millisecond timestamp, where 0 represents the start of the current node process.

performance.timeOrigin#

Added in: v8.5.0

The timeOrigin specifies the high resolution millisecond timestamp at which the current node process began, measured in Unix time.

performance.timerify(fn)#

Added in: v8.5.0

This property is an extension by Node.js. It is not available in Web browsers.

Wraps a function within a new function that measures the running time of the wrapped function. A PerformanceObserver must be subscribed to the 'function'event type in order for the timing details to be accessed.

const {
  performance,
  PerformanceObserver
} = require('perf_hooks');

function someFunction() {
  console.log('hello world');
}

const wrapped = performance.timerify(someFunction);

const obs = new PerformanceObserver((list) => {
  console.log(list.getEntries()[0].duration);
  obs.disconnect();
});
obs.observe({ entryTypes: ['function'] });

// A performance timeline entry will be created
wrapped();

Class: PerformanceEntry#

Added in: v8.5.0

performanceEntry.duration#

Added in: v8.5.0

The total number of milliseconds elapsed for this entry. This value will not be meaningful for all Performance Entry types.

performanceEntry.entryType#

Added in: v8.5.0

The type of the performance entry. It may be one of:

performanceEntry.flags#

Added in: v13.9.0, v12.17.0

This property is an extension by Node.js. It is not available in Web browsers.

When performanceEntry.entryType is equal to 'gc', the performance.flagsproperty contains additional information about garbage collection operation. The value may be one of:

performanceEntry.name#

Added in: v8.5.0

The name of the performance entry.

performanceEntry.kind#

Added in: v8.5.0

This property is an extension by Node.js. It is not available in Web browsers.

When performanceEntry.entryType is equal to 'gc', the performance.kindproperty identifies the type of garbage collection operation that occurred. The value may be one of:

performanceEntry.startTime#

Added in: v8.5.0

The high resolution millisecond timestamp marking the starting time of the Performance Entry.

Class: PerformanceNodeTiming#

Added in: v8.5.0

This property is an extension by Node.js. It is not available in Web browsers.

Provides timing details for Node.js itself. The constructor of this class is not exposed to users.

performanceNodeTiming.bootstrapComplete#

Added in: v8.5.0

The high resolution millisecond timestamp at which the Node.js process completed bootstrapping. If bootstrapping has not yet finished, the property has the value of -1.

performanceNodeTiming.environment#

Added in: v8.5.0

The high resolution millisecond timestamp at which the Node.js environment was initialized.

performanceNodeTiming.idleTime#

Added in: v14.10.0, v12.19.0

The high resolution millisecond timestamp of the amount of time the event loop has been idle within the event loop's event provider (e.g. epoll_wait). This does not take CPU usage into consideration. If the event loop has not yet started (e.g., in the first tick of the main script), the property has the value of 0.

performanceNodeTiming.loopExit#

Added in: v8.5.0

The high resolution millisecond timestamp at which the Node.js event loop exited. If the event loop has not yet exited, the property has the value of -1. It can only have a value of not -1 in a handler of the 'exit' event.

performanceNodeTiming.loopStart#

Added in: v8.5.0

The high resolution millisecond timestamp at which the Node.js event loop started. If the event loop has not yet started (e.g., in the first tick of the main script), the property has the value of -1.

performanceNodeTiming.nodeStart#

Added in: v8.5.0

The high resolution millisecond timestamp at which the Node.js process was initialized.

performanceNodeTiming.v8Start#

Added in: v8.5.0

The high resolution millisecond timestamp at which the V8 platform was initialized.

Class: perf_hooks.PerformanceObserver#

new PerformanceObserver(callback)#

Added in: v8.5.0

PerformanceObserver objects provide notifications when newPerformanceEntry instances have been added to the Performance Timeline.

const {
  performance,
  PerformanceObserver
} = require('perf_hooks');

const obs = new PerformanceObserver((list, observer) => {
  console.log(list.getEntries());
  observer.disconnect();
});
obs.observe({ entryTypes: ['mark'], buffered: true });

performance.mark('test');

Because PerformanceObserver instances introduce their own additional performance overhead, instances should not be left subscribed to notifications indefinitely. Users should disconnect observers as soon as they are no longer needed.

The callback is invoked when a PerformanceObserver is notified about new PerformanceEntry instances. The callback receives aPerformanceObserverEntryList instance and a reference to thePerformanceObserver.

performanceObserver.disconnect()#

Added in: v8.5.0

Disconnects the PerformanceObserver instance from all notifications.

performanceObserver.observe(options)#

Added in: v8.5.0

Subscribes the PerformanceObserver instance to notifications of newPerformanceEntry instances identified by options.entryTypes.

When options.buffered is false, the callback will be invoked once for every PerformanceEntry instance:

const {
  performance,
  PerformanceObserver
} = require('perf_hooks');

const obs = new PerformanceObserver((list, observer) => {
  // Called three times synchronously. `list` contains one item.
});
obs.observe({ entryTypes: ['mark'] });

for (let n = 0; n < 3; n++)
  performance.mark(`test${n}`);
const {
  performance,
  PerformanceObserver
} = require('perf_hooks');

const obs = new PerformanceObserver((list, observer) => {
  // Called once. `list` contains three items.
});
obs.observe({ entryTypes: ['mark'], buffered: true });

for (let n = 0; n < 3; n++)
  performance.mark(`test${n}`);

Class: PerformanceObserverEntryList#

Added in: v8.5.0

The PerformanceObserverEntryList class is used to provide access to thePerformanceEntry instances passed to a PerformanceObserver. The constructor of this class is not exposed to users.

performanceObserverEntryList.getEntries()#

Added in: v8.5.0

Returns a list of PerformanceEntry objects in chronological order with respect to performanceEntry.startTime.

const {
  performance,
  PerformanceObserver
} = require('perf_hooks');

const obs = new PerformanceObserver((perfObserverList, observer) => {
  console.log(perfObserverList.getEntries());
  /**
   * [
   *   PerformanceEntry {
   *     name: 'test',
   *     entryType: 'mark',
   *     startTime: 81.465639,
   *     duration: 0
   *   },
   *   PerformanceEntry {
   *     name: 'meow',
   *     entryType: 'mark',
   *     startTime: 81.860064,
   *     duration: 0
   *   }
   * ]
   */
  observer.disconnect();
});
obs.observe({ entryTypes: ['mark'], buffered: true });

performance.mark('test');
performance.mark('meow');

performanceObserverEntryList.getEntriesByName(name[, type])#

Added in: v8.5.0

Returns a list of PerformanceEntry objects in chronological order with respect to performanceEntry.startTime whose performanceEntry.name is equal to name, and optionally, whose performanceEntry.entryType is equal totype.

const {
  performance,
  PerformanceObserver
} = require('perf_hooks');

const obs = new PerformanceObserver((perfObserverList, observer) => {
  console.log(perfObserverList.getEntriesByName('meow'));
  /**
   * [
   *   PerformanceEntry {
   *     name: 'meow',
   *     entryType: 'mark',
   *     startTime: 98.545991,
   *     duration: 0
   *   }
   * ]
   */
  console.log(perfObserverList.getEntriesByName('nope')); // []

  console.log(perfObserverList.getEntriesByName('test', 'mark'));
  /**
   * [
   *   PerformanceEntry {
   *     name: 'test',
   *     entryType: 'mark',
   *     startTime: 63.518931,
   *     duration: 0
   *   }
   * ]
   */
  console.log(perfObserverList.getEntriesByName('test', 'measure')); // []
  observer.disconnect();
});
obs.observe({ entryTypes: ['mark', 'measure'], buffered: true });

performance.mark('test');
performance.mark('meow');

performanceObserverEntryList.getEntriesByType(type)#

Added in: v8.5.0

Returns a list of PerformanceEntry objects in chronological order with respect to performanceEntry.startTime whose performanceEntry.entryTypeis equal to type.

const {
  performance,
  PerformanceObserver
} = require('perf_hooks');

const obs = new PerformanceObserver((perfObserverList, observer) => {
  console.log(perfObserverList.getEntriesByType('mark'));
  /**
   * [
   *   PerformanceEntry {
   *     name: 'test',
   *     entryType: 'mark',
   *     startTime: 55.897834,
   *     duration: 0
   *   },
   *   PerformanceEntry {
   *     name: 'meow',
   *     entryType: 'mark',
   *     startTime: 56.350146,
   *     duration: 0
   *   }
   * ]
   */
  observer.disconnect();
});
obs.observe({ entryTypes: ['mark'], buffered: true });

performance.mark('test');
performance.mark('meow');

perf_hooks.createHistogram([options])#

Added in: v15.9.0

Returns a .

perf_hooks.monitorEventLoopDelay([options])#

Added in: v11.10.0

This property is an extension by Node.js. It is not available in Web browsers.

Creates an IntervalHistogram object that samples and reports the event loop delay over time. The delays will be reported in nanoseconds.

Using a timer to detect approximate event loop delay works because the execution of timers is tied specifically to the lifecycle of the libuv event loop. That is, a delay in the loop will cause a delay in the execution of the timer, and those delays are specifically what this API is intended to detect.

const { monitorEventLoopDelay } = require('perf_hooks');
const h = monitorEventLoopDelay({ resolution: 20 });
h.enable();
// Do something.
h.disable();
console.log(h.min);
console.log(h.max);
console.log(h.mean);
console.log(h.stddev);
console.log(h.percentiles);
console.log(h.percentile(50));
console.log(h.percentile(99));

Class: Histogram#

Added in: v11.10.0

histogram.exceeds#

Added in: v11.10.0

The number of times the event loop delay exceeded the maximum 1 hour event loop delay threshold.

histogram.max#

Added in: v11.10.0

The maximum recorded event loop delay.

histogram.mean#

Added in: v11.10.0

The mean of the recorded event loop delays.

histogram.min#

Added in: v11.10.0

The minimum recorded event loop delay.

histogram.percentile(percentile)#

Added in: v11.10.0

Returns the value at the given percentile.

histogram.percentiles#

Added in: v11.10.0

Returns a Map object detailing the accumulated percentile distribution.

histogram.reset()#

Added in: v11.10.0

Resets the collected histogram data.

histogram.stddev#

Added in: v11.10.0

The standard deviation of the recorded event loop delays.

Class: IntervalHistogram extends Histogram#

A Histogram that is periodically updated on a given interval.

histogram.disable()#

Added in: v11.10.0

Disables the update interval timer. Returns true if the timer was stopped, false if it was already stopped.

histogram.enable()#

Added in: v11.10.0

Enables the update interval timer. Returns true if the timer was started, false if it was already started.

Cloning an IntervalHistogram#

instances can be cloned via . On the receiving end, the histogram is cloned as a plain object that does not implement the enable() and disable() methods.

Class: RecordableHistogram extends Histogram#

Added in: v15.9.0

histogram.record(val)#

Added in: v15.9.0

histogram.recordDelta()#

Added in: v15.9.0

Calculates the amount of time (in nanoseconds) that has passed since the previous call to recordDelta() and records that amount in the histogram.

Examples#

Measuring the duration of async operations#

The following example uses the Async Hooks and Performance APIs to measure the actual duration of a Timeout operation (including the amount of time it took to execute the callback).

'use strict';
const async_hooks = require('async_hooks');
const {
  performance,
  PerformanceObserver
} = require('perf_hooks');

const set = new Set();
const hook = async_hooks.createHook({
  init(id, type) {
    if (type === 'Timeout') {
      performance.mark(`Timeout-${id}-Init`);
      set.add(id);
    }
  },
  destroy(id) {
    if (set.has(id)) {
      set.delete(id);
      performance.mark(`Timeout-${id}-Destroy`);
      performance.measure(`Timeout-${id}`,
                          `Timeout-${id}-Init`,
                          `Timeout-${id}-Destroy`);
    }
  }
});
hook.enable();

const obs = new PerformanceObserver((list, observer) => {
  console.log(list.getEntries()[0]);
  performance.clearMarks();
  observer.disconnect();
});
obs.observe({ entryTypes: ['measure'], buffered: true });

setTimeout(() => {}, 1000);

Measuring how long it takes to load dependencies#

The following example measures the duration of require() operations to load dependencies:

'use strict';
const {
  performance,
  PerformanceObserver
} = require('perf_hooks');
const mod = require('module');

// Monkey patch the require function
mod.Module.prototype.require =
  performance.timerify(mod.Module.prototype.require);
require = performance.timerify(require);

// Activate the observer
const obs = new PerformanceObserver((list) => {
  const entries = list.getEntries();
  entries.forEach((entry) => {
    console.log(`require('${entry[0]}')`, entry.duration);
  });
  obs.disconnect();
});
obs.observe({ entryTypes: ['function'], buffered: true });

require('some-module');