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Node.js v14.6.0-rc.3 Documentation
Table of Contents
Performance measurement APIs#
Source Code: lib/perf_hooks.js
This module provides an implementation of a subset of the W3C Web 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
#
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])
#
name
<string>
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])
#
name
<string>
Creates a new PerformanceMark
entry in the Performance Timeline. A
PerformanceMark
is a subclass of PerformanceEntry
whose
performanceEntry.entryType
is always 'mark'
, and whose
performanceEntry.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. A
PerformanceMeasure
is a subclass of PerformanceEntry
whose
performanceEntry.entryType
is always 'measure'
, and whose
performanceEntry.duration
measures the number of milliseconds elapsed since
startMark
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 PerformanceMark
in the Performance Timeline or any of the timestamp properties provided by the
PerformanceNodeTiming
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
#
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()
#
- Returns: <number>
Returns the current high resolution millisecond timestamp, where 0 represents
the start of the current node
process.
performance.timeOrigin
#
The timeOrigin
specifies the high resolution millisecond timestamp at
which the current node
process began, measured in Unix time.
performance.timerify(fn)
#
fn
<Function>
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
#
performanceEntry.duration
#
The total number of milliseconds elapsed for this entry. This value will not be meaningful for all Performance Entry types.
performanceEntry.name
#
The name of the performance entry.
performanceEntry.startTime
#
The high resolution millisecond timestamp marking the starting time of the Performance Entry.
performanceEntry.entryType
#
The type of the performance entry. It may be one of:
'node'
(Node.js only)'mark'
(available on the Web)'measure'
(available on the Web)'gc'
(Node.js only)'function'
(Node.js only)'http2'
(Node.js only)'http'
(Node.js only)
performanceEntry.kind
#
This property is an extension by Node.js. It is not available in Web browsers.
When performanceEntry.entryType
is equal to 'gc'
, the performance.kind
property identifies the type of garbage collection operation that occurred.
The value may be one of:
perf_hooks.constants.NODE_PERFORMANCE_GC_MAJOR
perf_hooks.constants.NODE_PERFORMANCE_GC_MINOR
perf_hooks.constants.NODE_PERFORMANCE_GC_INCREMENTAL
perf_hooks.constants.NODE_PERFORMANCE_GC_WEAKCB
performanceEntry.flags#
This property is an extension by Node.js. It is not available in Web browsers.
When performanceEntry.entryType
is equal to 'gc'
, the performance.flags
property contains additional information about garbage collection operation.
The value may be one of:
perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_NO
perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_CONSTRUCT_RETAINED
perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_FORCED
perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_SYNCHRONOUS_PHANTOM_PROCESSING
perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_ALL_AVAILABLE_GARBAGE
perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_ALL_EXTERNAL_MEMORY
perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_SCHEDULE_IDLE
Class: PerformanceNodeTiming extends PerformanceEntry
#
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
#
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
#
The high resolution millisecond timestamp at which the Node.js environment was initialized.
performanceNodeTiming.loopExit
#
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
#
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
#
The high resolution millisecond timestamp at which the Node.js process was initialized.
performanceNodeTiming.v8Start
#
The high resolution millisecond timestamp at which the V8 platform was initialized.
Class: perf_hooks.PerformanceObserver
#
new PerformanceObserver(callback)
#
-
callback
<Function>list
<PerformanceObserverEntryList>observer
<PerformanceObserver>
PerformanceObserver
objects provide notifications when new
PerformanceEntry
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 a
PerformanceObserverEntryList
instance and a reference to the
PerformanceObserver
.
performanceObserver.disconnect()
#
Disconnects the PerformanceObserver
instance from all notifications.
performanceObserver.observe(options)
#
-
options
<Object>entryTypes
<string[]> An array of strings identifying the types ofPerformanceEntry
instances the observer is interested in. If not provided an error will be thrown.buffered
<boolean> If true, the notification callback will be called usingsetImmediate()
and multiplePerformanceEntry
instance notifications will be buffered internally. Iffalse
, notifications will be immediate and synchronous. Default:false
.
Subscribes the PerformanceObserver
instance to notifications of new
PerformanceEntry
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
#
The PerformanceObserverEntryList
class is used to provide access to the
PerformanceEntry
instances passed to a PerformanceObserver
.
The constructor of this class is not exposed to users.
performanceObserverEntryList.getEntries()
#
- Returns: <PerformanceEntry[]>
Returns a list of PerformanceEntry
objects in chronological order
with respect to performanceEntry.startTime
.
performanceObserverEntryList.getEntriesByName(name[, type])
#
name
<string>type
<string>- Returns: <PerformanceEntry[]>
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 to
type
.
performanceObserverEntryList.getEntriesByType(type)
#
type
<string>- Returns: <PerformanceEntry[]>
Returns a list of PerformanceEntry
objects in chronological order
with respect to performanceEntry.startTime
whose performanceEntry.entryType
is equal to type
.
perf_hooks.monitorEventLoopDelay([options])
#
-
options
<Object>resolution
<number> The sampling rate in milliseconds. Must be greater than zero. Default:10
.
- Returns: <Histogram>
This property is an extension by Node.js. It is not available in Web browsers.
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
#
Tracks the event loop delay at a given sampling rate. The constructor of this class not exposed to users.
This property is an extension by Node.js. It is not available in Web browsers.
histogram.disable()
#
- Returns: <boolean>
Disables the event loop delay sample timer. Returns true
if the timer was
stopped, false
if it was already stopped.
histogram.enable()
#
- Returns: <boolean>
Enables the event loop delay sample timer. Returns true
if the timer was
started, false
if it was already started.
histogram.exceeds
#
The number of times the event loop delay exceeded the maximum 1 hour event loop delay threshold.
histogram.max
#
The maximum recorded event loop delay.
histogram.mean
#
The mean of the recorded event loop delays.
histogram.min
#
The minimum recorded event loop delay.
histogram.percentile(percentile)
#
Returns the value at the given percentile.
histogram.percentiles
#
Returns a Map
object detailing the accumulated percentile distribution.
histogram.reset()
#
Resets the collected histogram data.
histogram.stddev
#
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');