Performance Timing API | Node.js v13.14.0 Documentation (original) (raw)

Performance Timing API#

The Performance Timing API provides an implementation of theW3C Performance Timeline specification. The purpose of the API is to support collection of high resolution performance metrics. This is the same Performance API as implemented in modern Web browsers.

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');
});

Class: Performance#

Added in: v8.5.0

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.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

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

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.name#

Added in: v8.5.0

The name of the performance entry.

performanceEntry.startTime#

Added in: v8.5.0

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

performanceEntry.entryType#

Added in: v8.5.0

The type of the performance entry. Currently it may be one of: 'node','mark', 'measure', 'gc', 'function', 'http2' or 'http'.

performanceEntry.kind#

Added in: v8.5.0

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.flags#

Added in: v13.9.0

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

Class: PerformanceNodeTiming extends PerformanceEntry#

Added in: v8.5.0

Provides timing details for Node.js itself.

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.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: 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.

performanceObserverEntryList.getEntries()#

Added in: v8.5.0

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

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.

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.

perf_hooks.monitorEventLoopDelay([options])#

Added in: v11.10.0

Creates a Histogram 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

Tracks the event loop delay at a given sampling rate.

histogram.disable()#

Added in: v11.10.0

Disables the event loop delay sample timer. Returns true if the timer was stopped, false if it was already stopped.

histogram.enable()#

Added in: v11.10.0

Enables the event loop delay sample timer. Returns true if the timer was started, false if it was already started.

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.

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');