Performance measurement APIs

Added in: v8.5.0

源代码: 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:

• High Resolution Time
• Performance Timeline
• User Timing
• Resource Timing

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M 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.

M performance.clearMarks([name])

Added in: v8.5.0

• name string

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

M performance.clearMeasures([name])

Added in: v16.7.0

• name string

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

M performance.clearResourceTimings([name])

Added in: v18.2.0

• name string

If name is not provided, removes all PerformanceResourceTiming objects from the Resource Timeline. If name is provided, removes only the named resource.

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

Added in: v14.10.0, v12.19.0

• utilization1 Object The result of a previous call to eventLoopUtilization().
• utilization2 Object The result of a previous call to eventLoopUtilization() prior to utilization1.
• Returns Object
  • idle number
  • active number
  • utilization number

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 active and 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.

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

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

M performance.getEntries()

Added in: v16.7.0

• Returns: PerformanceEntry[]

Returns a list of PerformanceEntry objects in chronological order with respect to performanceEntry.startTime. If you are only interested in performance entries of certain types or that have certain names, see performance.getEntriesByType() and performance.getEntriesByName().

M performance.getEntriesByName(name[, type])

Added in: v16.7.0

• 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.

M performance.getEntriesByType(type)

Added in: v16.7.0

• 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.

M performance.mark([name[, options]])

• name string
• options Object
  • detail any Additional optional detail to include with the mark.
  • startTime number An optional timestamp to be used as the mark time. Default: performance.now().

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.

The created PerformanceMark entry is put in the global Performance Timeline and can be queried with performance.getEntries, performance.getEntriesByName, and performance.getEntriesByType. When the observation is performed, the entries should be cleared from the global Performance Timeline manually with performance.clearMarks.

M performance.markResourceTiming(timingInfo, requestedUrl, initiatorType, global, cacheMode)

Added in: v18.2.0

• timingInfo Object Fetch Timing Info
• requestedUrl string The resource url
• initiatorType string The initiator name, e.g: 'fetch'
• global Object
• cacheMode string The cache mode must be an empty string ('') or 'local'

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

Creates a new PerformanceResourceTiming entry in the Resource Timeline. A PerformanceResourceTiming is a subclass of PerformanceEntry whose performanceEntry.entryType is always 'resource'. Performance resources are used to mark moments in the Resource Timeline.

The created PerformanceMark entry is put in the global Resource Timeline and can be queried with performance.getEntries, performance.getEntriesByName, and performance.getEntriesByType. When the observation is performed, the entries should be cleared from the global Performance Timeline manually with performance.clearResourceTimings.

M performance.measure(name[, startMarkOrOptions[, endMark]])

• name string
• startMarkOrOptions string | Object Optional.
  • detail any Additional optional detail to include with the measure.
  • duration number Duration between start and end times.
  • end number | string Timestamp to be used as the end time, or a string identifying a previously recorded mark.
  • start number | string Timestamp to be used as the start time, or a string identifying a previously recorded mark.
• endMark string Optional. Must be omitted if startMarkOrOptions is an Object.

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, an error is thrown.

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.

The created PerformanceMeasure entry is put in the global Performance Timeline and can be queried with performance.getEntries, performance.getEntriesByName, and performance.getEntriesByType. When the observation is performed, the entries should be cleared from the global Performance Timeline manually with performance.clearMeasures.

M performance.nodeTiming

Added in: v8.5.0

• PerformanceNodeTiming

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.

M performance.now()

Added in: v8.5.0

• Returns: number

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

M performance.setResourceTimingBufferSize(maxSize)

Added in: v18.8.0

Sets the global performance resource timing buffer size to the specified number of "resource" type performance entry objects.

By default the max buffer size is set to 250.

M performance.timeOrigin

Added in: v8.5.0

• number

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

M performance.timerify(fn[, options])

• fn Function
• options Object
  • histogram RecordableHistogram A histogram object created using perf_hooks.createHistogram() that will record runtime durations in nanoseconds.

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.

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If the wrapped function returns a promise, a finally handler will be attached to the promise and the duration will be reported once the finally handler is invoked.

M performance.toJSON()

Added in: v16.1.0

An object which is JSON representation of the performance object. It is similar to window.performance.toJSON in browsers.

E 'resourcetimingbufferfull'

Added in: v18.8.0

The 'resourcetimingbufferfull' event is fired when the global performance resource timing buffer is full. Adjust resource timing buffer size with performance.setResourceTimingBufferSize() or clear the buffer with performance.clearResourceTimings() in the event listener to allow more entries to be added to the performance timeline buffer.

C PerformanceEntry

Added in: v8.5.0

M performanceEntry.detail

Added in: v16.0.0

• any

Additional detail specific to the entryType.

M performanceEntry.duration

Added in: v8.5.0

• number

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

M performanceEntry.entryType

Added in: v8.5.0

• string

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)

M performanceEntry.flags

• number

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

M performanceEntry.name

Added in: v8.5.0

• string

The name of the performance entry.

M performanceEntry.kind

• number

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

M performanceEntry.startTime

Added in: v8.5.0

• number

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

Garbage Collection ('gc') Details

When performanceEntry.type is equal to 'gc', the performanceEntry.detail property will be an Object with two properties:

• kind number 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
• flags number 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

HTTP ('http') Details

When performanceEntry.type is equal to 'http', the performanceEntry.detail property will be an Object containing additional information.

If performanceEntry.name is equal to HttpClient, the detail will contain the following properties: req, res. And the req property will be an Object containing method, url, headers, the res property will be an Object containing statusCode, statusMessage, headers.

If performanceEntry.name is equal to HttpRequest, the detail will contain the following properties: req, res. And the req property will be an Object containing method, url, headers, the res property will be an Object containing statusCode, statusMessage, headers.

This could add additional memory overhead and should only be used for diagnostic purposes, not left turned on in production by default.

HTTP/2 ('http2') Details

When performanceEntry.type is equal to 'http2', the performanceEntry.detail property will be an Object containing additional performance information.

If performanceEntry.name is equal to Http2Stream, the detail will contain the following properties:

• bytesRead number The number of DATA frame bytes received for this Http2Stream.
• bytesWritten number The number of DATA frame bytes sent for this Http2Stream.
• id number The identifier of the associated Http2Stream
• timeToFirstByte number The number of milliseconds elapsed between the PerformanceEntry startTime and the reception of the first DATA frame.
• timeToFirstByteSent number The number of milliseconds elapsed between the PerformanceEntry startTime and sending of the first DATA frame.
• timeToFirstHeader number The number of milliseconds elapsed between the PerformanceEntry startTime and the reception of the first header.

If performanceEntry.name is equal to Http2Session, the detail will contain the following properties:

• bytesRead number The number of bytes received for this Http2Session.
• bytesWritten number The number of bytes sent for this Http2Session.
• framesReceived number The number of HTTP/2 frames received by the Http2Session.
• framesSent number The number of HTTP/2 frames sent by the Http2Session.
• maxConcurrentStreams number The maximum number of streams concurrently open during the lifetime of the Http2Session.
• pingRTT number The number of milliseconds elapsed since the transmission of a PING frame and the reception of its acknowledgment. Only present if a PING frame has been sent on the Http2Session.
• streamAverageDuration number The average duration (in milliseconds) for all Http2Stream instances.
• streamCount number The number of Http2Stream instances processed by the Http2Session.
• type string Either 'server' or 'client' to identify the type of Http2Session.

Timerify ('function') Details

When performanceEntry.type is equal to 'function', the performanceEntry.detail property will be an Array listing the input arguments to the timed function.

Net ('net') Details

When performanceEntry.type is equal to 'net', the performanceEntry.detail property will be an Object containing additional information.

If performanceEntry.name is equal to connect, the detail will contain the following properties: host, port.

DNS ('dns') Details

When performanceEntry.type is equal to 'dns', the performanceEntry.detail property will be an Object containing additional information.

If performanceEntry.name is equal to lookup, the detail will contain the following properties: hostname, family, hints, verbatim, addresses.

If performanceEntry.name is equal to lookupService, the detail will contain the following properties: host, port, hostname, service.

If performanceEntry.name is equal to queryxxx or getHostByAddr, the detail will contain the following properties: host, ttl, result. The value of result is same as the result of queryxxx or getHostByAddr.

C PerformanceNodeTiming

Added in: v8.5.0

• 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.

M performanceNodeTiming.bootstrapComplete

Added in: v8.5.0

• number

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.

M performanceNodeTiming.environment

Added in: v8.5.0

• number

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

M performanceNodeTiming.idleTime

Added in: v14.10.0, v12.19.0

• number

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.

M performanceNodeTiming.loopExit

Added in: v8.5.0

• number

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.

M performanceNodeTiming.loopStart

Added in: v8.5.0

• number

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.

M performanceNodeTiming.nodeStart

Added in: v8.5.0

• number

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

M performanceNodeTiming.v8Start

Added in: v8.5.0

• number

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

C PerformanceResourceTiming

Added in: v18.2.0

• Extends: PerformanceEntry

Provides detailed network timing data regarding the loading of an application's resources.

The constructor of this class is not exposed to users directly.

M performanceResourceTiming.workerStart

Added in: v18.2.0

• number

The high resolution millisecond timestamp at immediately before dispatching the fetch request. If the resource is not intercepted by a worker the property will always return 0.

M performanceResourceTiming.redirectStart

Added in: v18.2.0

• number

The high resolution millisecond timestamp that represents the start time of the fetch which initiates the redirect.

M performanceResourceTiming.redirectEnd

Added in: v18.2.0

• number

The high resolution millisecond timestamp that will be created immediately after receiving the last byte of the response of the last redirect.

M performanceResourceTiming.fetchStart

Added in: v18.2.0

• number

The high resolution millisecond timestamp immediately before the Node.js starts to fetch the resource.

M performanceResourceTiming.domainLookupStart

Added in: v18.2.0

• number

The high resolution millisecond timestamp immediately before the Node.js starts the domain name lookup for the resource.

M performanceResourceTiming.domainLookupEnd

Added in: v18.2.0

• number

The high resolution millisecond timestamp representing the time immediately after the Node.js finished the domain name lookup for the resource.

M performanceResourceTiming.connectStart

Added in: v18.2.0

• number

The high resolution millisecond timestamp representing the time immediately before Node.js starts to establish the connection to the server to retrieve the resource.

M performanceResourceTiming.connectEnd

Added in: v18.2.0

• number

The high resolution millisecond timestamp representing the time immediately after Node.js finishes establishing the connection to the server to retrieve the resource.

M performanceResourceTiming.secureConnectionStart

Added in: v18.2.0

• number

The high resolution millisecond timestamp representing the time immediately before Node.js starts the handshake process to secure the current connection.

M performanceResourceTiming.requestStart

Added in: v18.2.0

• number

The high resolution millisecond timestamp representing the time immediately before Node.js receives the first byte of the response from the server.

M performanceResourceTiming.responseEnd

Added in: v18.2.0

• number

The high resolution millisecond timestamp representing the time immediately after Node.js receives the last byte of the resource or immediately before the transport connection is closed, whichever comes first.

M performanceResourceTiming.transferSize

Added in: v18.2.0

• number

A number representing the size (in octets) of the fetched resource. The size includes the response header fields plus the response payload body.

M performanceResourceTiming.encodedBodySize

Added in: v18.2.0

• number

A number representing the size (in octets) received from the fetch (HTTP or cache), of the payload body, before removing any applied content-codings.

M performanceResourceTiming.decodedBodySize

Added in: v18.2.0

• number

A number representing the size (in octets) received from the fetch (HTTP or cache), of the message body, after removing any applied content-codings.

M performanceResourceTiming.toJSON()

Added in: v18.2.0

Returns a object that is the JSON representation of the PerformanceResourceTiming object

C perf_hooks.PerformanceObserver

M new PerformanceObserver(callback)

• callback Function
  • list PerformanceObserverEntryList
  • observer PerformanceObserver

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

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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.

M performanceObserver.disconnect()

Added in: v8.5.0

Disconnects the PerformanceObserver instance from all notifications.

M performanceObserver.observe(options)

• options Object
  • type string A single PerformanceEntry type. Must not be given if entryTypes is already specified.
  • entryTypes string[] An array of strings identifying the types of PerformanceEntry instances the observer is interested in. If not provided an error will be thrown.
  • buffered boolean If true, the observer callback is called with a list global PerformanceEntry buffered entries. If false, only PerformanceEntrys created after the time point are sent to the observer callback. Default: false.

Subscribes the PerformanceObserver instance to notifications of new PerformanceEntry instances identified either by options.entryTypes or options.type:

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C PerformanceObserverEntryList

Added in: v8.5.0

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.

M performanceObserverEntryList.getEntries()

Added in: v8.5.0

• Returns: PerformanceEntry[]

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

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M performanceObserverEntryList.getEntriesByName(name[, type])

Added in: v8.5.0

• 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.

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M performanceObserverEntryList.getEntriesByType(type)

Added in: v8.5.0

• 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.

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M perf_hooks.createHistogram([options])

Added in: v15.9.0, v14.18.0

• options Object
  • lowest number | bigint The lowest discernible value. Must be an integer value greater than 0. Default: 1.
  • highest number | bigint The highest recordable value. Must be an integer value that is equal to or greater than two times lowest. Default: Number.MAX_SAFE_INTEGER.
  • figures number The number of accuracy digits. Must be a number between 1 and 5. Default: 3.
• Returns RecordableHistogram

Returns a RecordableHistogram.

M perf_hooks.monitorEventLoopDelay([options])

Added in: v11.10.0

• options Object
  • resolution number The sampling rate in milliseconds. Must be greater than zero. Default: 10.
• Returns: IntervalHistogram

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.

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C Histogram

Added in: v11.10.0

M histogram.count

Added in: v17.4.0, v16.14.0

• number

The number of samples recorded by the histogram.

M histogram.countBigInt

Added in: v17.4.0, v16.14.0

• bigint

The number of samples recorded by the histogram.

M histogram.exceeds

Added in: v11.10.0

• number

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

M histogram.exceedsBigInt

Added in: v17.4.0, v16.14.0

• bigint

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

M histogram.max

Added in: v11.10.0

• number

The maximum recorded event loop delay.

M histogram.maxBigInt

Added in: v17.4.0, v16.14.0

• bigint

The maximum recorded event loop delay.

M histogram.mean

Added in: v11.10.0

• number

The mean of the recorded event loop delays.

M histogram.min

Added in: v11.10.0

• number

The minimum recorded event loop delay.

M histogram.minBigInt

Added in: v17.4.0, v16.14.0

• bigint

The minimum recorded event loop delay.

M histogram.percentile(percentile)

Added in: v11.10.0

• percentile number A percentile value in the range (0, 100].
• Returns: number

Returns the value at the given percentile.

M histogram.percentileBigInt(percentile)

Added in: v17.4.0, v16.14.0

• percentile number A percentile value in the range (0, 100].
• Returns: bigint

Returns the value at the given percentile.

M histogram.percentiles

Added in: v11.10.0

• Map

Returns a Map object detailing the accumulated percentile distribution.

M histogram.percentilesBigInt

Added in: v17.4.0, v16.14.0

• Map

Returns a Map object detailing the accumulated percentile distribution.

M histogram.reset()

Added in: v11.10.0

Resets the collected histogram data.

M histogram.stddev

Added in: v11.10.0

• number

The standard deviation of the recorded event loop delays.

C IntervalHistogram extends Histogram

A Histogram that is periodically updated on a given interval.

M histogram.disable()

Added in: v11.10.0

• Returns: boolean

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

M histogram.enable()

Added in: v11.10.0

• Returns: boolean

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

Cloning an IntervalHistogram

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

C RecordableHistogram extends Histogram

Added in: v15.9.0, v14.18.0

M histogram.add(other)

Added in: v17.4.0, v16.14.0

• other RecordableHistogram

Adds the values from other to this histogram.

M histogram.record(val)

Added in: v15.9.0, v14.18.0

• val number | bigint The amount to record in the histogram.

M histogram.recordDelta()

Added in: v15.9.0, v14.18.0

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).

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Measuring how long it takes to load dependencies

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

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Measuring how long one HTTP round-trip takes

The following example is used to trace the time spent by HTTP client (OutgoingMessage) and HTTP request (IncomingMessage). For HTTP client, it means the time interval between starting the request and receiving the response, and for HTTP request, it means the time interval between receiving the request and sending the response:

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Measuring how long the net.connect (only for TCP) takes when the connection is successful

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Measuring how long the DNS takes when the request is successful

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