Performance Timeline

Editor's Draft October 23, 2013

This version:
http://dvcs.w3.org/hg/webperf/raw-file/tip/specs/PerformanceTimeline/Overview.html
Latest version:
http://www.w3.org/TR/performance-timeline/
Latest Editor's Draft:
http://dvcs.w3.org/hg/webperf/raw-file/tip/specs/PerformanceTimeline/Overview.html
Previous versions:
http://www.w3.org/TR/2012/CR-performance-timeline-20120726/
http://www.w3.org/TR/2012/WD-performance-timeline-20120508/
Editors:
Jatinder Mann, Microsoft Corp., <>
Zhiheng Wang, Google Inc. (Until July 2013)

Abstract

This specification defines an unified interface to store and retrieve performance metric data. This specification does not cover individual performance metric interfaces.

Status of this document

This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.

This is a work in progress and may change without any notices.

Please send comments to public-web-perf@w3.org (archived) with [PerformanceTimeline] at the start of the subject line.

This document is produced by the Web Performance Working Group. The Web Performance Working Group is part of the Rich Web Clients Activity in the W3C Interaction Domain.

Publication as a Working Draft does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.

This document was produced by a group operating under the 5 February 2004 W3C Patent Policy. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.

Table of Contents

  1. 1 Introduction
  2. 2 Conformance requirements
  3. 3 Terminology
  4. 4 Performance Timeline
    1. 4.1 The Performance Timeline
    2. 4.2 The PerformanceEntry interface
    3. 4.3 Extensions to the Performance interface
    4. 4.4 Vendor Extensions
  5. 5 References
  6. Acknowledgements

1 Introduction

This section is non-normative.

Accurately measuring performance characteristics of web applications is an important aspect of making web applications faster. [Navigation Timing], [Resource Timing], and [User Timing] are examples of specifications that define timing information related to the navigation of the document, resources on the page, and developer scripts, respectively.

Together these interfaces, and potentially others created in the future, define performance metrics that describe the performance timeline of a web application. This specification provides an unifying interface to access and retrieve these various performance metrics from the performance timeline of a web application.

The following script shows how a developer can use the PerformanceEntry interface to obtain timing data related to the navigation of the document, resources on the page and developer scripts.

<!doctype html>
<html>
  <head>
  </head>
  <body onload="init()">
    <img id="image0" src="http://www.w3.org/Icons/w3c_main.png" />
    <script>
       function init() 
       {
            performance.mark("startWork"); // see [User Timing]
            doWork(); // Some developer code
            performance.mark("endWork");
            
            measurePerf();
       }

       function measurePerf() 
       {
           var perfEntries = performance.getEntries();
           for (var i = 0; i < perfEntries.length; i++)
           {
                 if (window.console) console.log("Name: "        + perfEntries[i].name      + 
                                                 " Entry Type: " + perfEntries[i].entryType +
                                                 " Start Time: " + perfEntries[i].startTime + 
                                                 " Duration: "   + perfEntries[i].duration  + "\n");
           }
       }
    </script>
  </body>
</html>

2 Conformance requirements

All diagrams, examples, and notes in this specification are non-normative, as are all sections explicitly marked non-normative. Everything else in this specification is normative.

The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in the normative parts of this document are to be interpreted as described in RFC 2119. For readability, these words do not appear in all uppercase letters in this specification.

Requirements phrased in the imperative as part of algorithms (such as "strip any leading space characters" or "return false and abort these steps") are to be interpreted with the meaning of the key word ("must", "should", "may", etc) used in introducing the algorithm.

Some conformance requirements are phrased as requirements on attributes, methods or objects. Such requirements are to be interpreted as requirements on user agents.

Conformance requirements phrased as algorithms or specific steps may be implemented in any manner, so long as the end result is equivalent. (In particular, the algorithms defined in this specification are intended to be easy to follow, and not intended to be performant.)

The IDL fragments in this specification must be interpreted as required for conforming IDL fragments, as described in the Web IDL specification. [Web IDL]

3 Terminology

The construction "a Foo object", where Foo is actually an interface, is sometimes used instead of the more accurate "an object implementing the interface Foo".

Throughout this work, all time values are measured in milliseconds since the start of navigation of the document. For example, the start of navigation of the document occurs at time 0. The term current time refers to the number of milliseconds since the start of navigation of the document until the current moment in time. This definition of time is based on the High Resolution Time specification [High Resolution Time] and is different from the definition of time used in the Navigation Timing specification [Navigation Timing], where time is measured in milliseconds since midnight of January 1, 1970 (UTC).

4 Performance Timeline

4.1 The Performance Timeline

All interfaces that participate in the Performance Timeline, such as the PerformanceResourceTiming [Resource Timing], PerformanceMark, and PerformanceMeasure [User Timing] interfaces, must adhere to the following rules:

4.2 The PerformanceEntry interface

interface PerformanceEntry {
  readonly attribute DOMString name;
  readonly attribute DOMString entryType;
  readonly attribute DOMHighResTimeStamp startTime;
  readonly attribute DOMHighResTimeStamp duration;
};

name attribute

The name attribute must return the identifier for this PerformanceEntry object. This identifier does not have to be unique.

entryType attribute

The entryType attribute must return a DOMString that describes the type of the interface represented by this PerformanceEntry object.

Note

The Web Performance/entryType wiki page lists all of the known entryType values.

startTime attribute

The startTime attribute must return a DOMHighResTimeStamp that contains the time value of the first recorded timestamp of this performance metric.

duration attribute

The duration attribute must return a DOMHighResTimeStamp that contains the time value of the duration of the entire event being recorded by this PerformanceEntry. Typically, this would be the time difference between the last recorded timestamp and the first recorded timestamp of this PerformanceEntry. A performance metric may choose to return a duration of 0, if the duration concept doesn't apply.

4.3 Extensions to the Performance interface

partial interface Performance {
  PerformanceEntryList getEntries();
  PerformanceEntryList getEntriesByType(DOMString entryType);
  PerformanceEntryList getEntriesByName(DOMString name, optional DOMString entryType);
};

typedef sequence <PerformanceEntry> PerformanceEntryList;

The window.performance attribute provides a hosting area for performance measurement related attributes and methods using the Performance interface [Navigation Timing].

getEntries method

The getEntries method returns a PerformanceEntryList object that contains a copy of all PerformanceEntry objects in chronological order with respect to startTime.

No parameters

Return value

A PerformanceEntryList object.

No exceptions

getEntriesByType method

The getEntriesByType method returns a PerformanceEntryList object that contains a copy of all PerformanceEntry objects, in chronological order with respect to startTime, that have the same value for the entryType attribute of PerformanceEntry as the entryType parameter.

Parameter

DOMString entryType

A PerformanceEntryList object that contains a copy of PerformanceEntry objects that have the same value for the entryType attribute of PerformanceEntry as the entryType parameter. If no such PerformanceEntry objects exist, the PerformanceEntryList must be empty.

Return value

A PerformanceEntryList object.

No exceptions

getEntriesByName method

The getEntriesByName method returns a PerformanceEntryList object that contains a copy of PerformanceEntry objects, in chronological order with respect to startTime, that have the same value for the name attribute of PerformanceEntry as the name parameter and, if specified, have the same value for the entryType attribute of PerformanceEntry as the entryType parameter.

Parameter

DOMString name

The PerformanceEntryList object that contains a copy of PerformanceEntry objects that have the same value for the name attribute of PerformanceEntry as the name parameter. If no such PerformanceEntry objects exist, the PerformanceEntryList must be empty.

DOMString entryType

The PerformanceEntryList object that only contains a copy of PerformanceEntry objects that have the same value for the entryType attribute of PerformanceEntry as the entryType parameter and have the same value for the name attribute of PerformanceEntry as the name parameter. If no such PerformanceEntry objects exist, the PerformanceEntryList must be empty.

Return value

A PerformanceEntryList object.

No exceptions

4.4 Vendor Extensions

If a vendor-specific proprietary user agent extension is needed to create experimental PerformanceEntry objects, on getting the entryType IDL attribute, vendors MUST return a DOMString that uses the following convention:

[vendorprefix]-[entrytype]

Where,

5 References

5.1 Normative References

[IETF RFC 2119]
Key words for use in RFCs to Indicate Requirement Levels, Scott Bradner, Author. Internet Engineering Task Force, March 1997. Available at http://www.ietf.org/rfc/rfc2119.txt.
[Navigation Timing]
Navigation Timing, Zhiheng Wang, Editor. W3C Recommendation, World Wide Web Consortium, December 2012. This version of the Navigation Timing specification is available from http://www.w3.org/TR/2012/REC-navigation-timing-20121217/. The latest version of Navigation Timing is available at http://www.w3.org/TR/navigation-timing/.
[High Resolution Time]
High Resolution Time, Jatinder Mann, Editor. W3C Recommendation, World Wide Web Consortium, December 2012. This version of the High Resolution Time specification is available from http://www.w3.org/TR/2012/REC-hr-time-20121217/. The latest version of High Resolution Time is available at http://www.w3.org/TR/hr-time/.
[Web IDL]
Web IDL, Cameron McCormack, Editor. World Wide Web Consortium, April 2012. This version of the Web IDL specification is available from http://www.w3.org/TR/2012/CR-WebIDL-20120419/. The latest version of Web IDL is available at http://www.w3.org/TR/WebIDL/.

5.1 Informative References

[User Timing]
User Timing, J. Mann, Z. Wang, et al. Editors. World Wide Web Consortium, July 2012. This version of the User Timing specification is available from http://www.w3.org/TR/2012/CR-user-timing-20120726/. The latest version of User Timing is available at http://www.w3.org/TR/user-timing/.
[Resource Timing]
Resource Timing, J. Mann, Z. Wang, et al. Editors. World Wide Web Consortium, May 2012. This version of the Resource Timing specification is available from http://www.w3.org/TR/2012/CR-resource-timing-20120522/. The latest version of Resource Timing is available at http://www.w3.org/TR/user-timing/.

Acknowledgements

We would like to offer our sincere thanks to all the people that we have been in touch with regarding this draft for their reviews and feedback.