W3C home > Mailing lists > Public > public-web-perf@w3.org > February 2011

Re: [UserTiming] Feedback on latest draft

From: Tony Gentilcore <tonyg@google.com>
Date: Mon, 31 Jan 2011 21:02:56 -0800
Message-ID: <AANLkTik_dt3-UqJu8aHOZmaijJMC=wmC5XfLL3TQaXoB@mail.gmail.com>
To: Anderson Quach <aquach@microsoft.com>
Cc: public-web-perf <public-web-perf@w3.org>
Excellent summary. I'd like to consider a much simpler interface.
Justifications inline below.

  [Supplemental]
  interface PerformanceTiming {
    // Returns Object with string keys and array of numbers values.
    readonly attribute Object marks;
  };

  [Supplemental]
  interface Performance {
    // TBD: Standardize a set of universally applicable mark names
appropriate for passing to mark().
    const string MARK_FULLY_VISIBLE = "fullyVisible";
    const string MARK_FULLY_INTERACTIVE = "fullyInteractive";

    void mark(in DOMString name);
    void clearMarks();
  };

On Thu, Jan 27, 2011 at 4:58 PM, Anderson Quach <aquach@microsoft.com>wrote:

> *User Timing*
>
>
>
> The IE-9 Beta has a running implementation of the first draft [1] available
> here [2].
>
>
>
> Requirements discussed
>
> ·         R1: High precision marks accessible by mark name, within 1ms
> accuracy
>
> ·         R2: Ease of store and access of marks
>
> ·         R3: Does not burden the browser, efficient use of CPU and Memory
>
>
>
> Use cases discussed
>
> ·         UC1: A web developer makes unique marks in their web-page /
> web-app.
>
> ·         UC2: A web developer uses marks in repeated or iterative
> patterns. For example, a web developer may want to measure successive clicks
> denoted by a single name called “my_action”.
>
> ·         UC3: Analytics companies report on standardized markers
>
> ·         UC4: Developer tools consume user marks interface
>
>
>
> Nice to have, as discussed
>
> ·         NH1: Measures – achievable through JavaScript, we can create a
> best practice library that leverages the implementation of mark to create
> measures, which is a delta between marks and/or a date time.
>
>
>
> With the latest User Timing spec [3] we have the following concerns.
>
>
>
> *Issue 1 – Does not meet UC2.*
>
> The ‘.user’ attribute currently does not support the ability to retrieve a
> list of marks to meet Use Case 2 (UC2).  The getMarks() API solves this by
> returning an array of all marks that match that name.  The web-developer can
> get the latest single mark using getMark().
>

Multiple marks under the same name seems like an important requirement.
However, I think that is orthogonal to whether we choose an attribute or
method to expose it. For instance, .marks could expose an object with string
keys and array of numbers values.

console.log(performance.timing.marks)
>> {
  fullyLoaded: [123456789],
  widgetClicked: [123456790, 1234567891]
}

It would be easy to understand as developers already know how to work with
objects and we wouldn't have to implement custom getters. For instance:

console.log(performance.timing.marks.fullyLoaded)
>> [123456789]
console.log(performance.timing.marks["widgetClicked"])
>> [123456790, 1234567891]

Also, since it is already JSON, it is trivial to ping home and more compact
than the getMarks() proposal. Compare the size difference:

console.log(performance.getMarks())
>> [{name: "fullyLoaded", time: 123456789}, {name: "widgetClicked", time: 123456790}, {name:
"widgetClicked", time: 1234567891}]

console.log(performance.timing.marks)
>>{fullyLoaded: [123456789], widgetClicked: [123456790, 1234567891]}


>
> *Issue 2 – Ease of use, possible confusion*
>
> *Assuming we support the ability to retrieve multiple marks from the same
> name.
>
>
>
> If we change from the getMark()/getMarks() API to a '.user' attribute,
> we're overloading that attribute getter for multiple use cases: filtering
> and indexing.  This might lead to confusion.
>
>
> For example:
>
> Use Cases
>
> getMark()/getMarks()
>
> .userTiming attribute
>
> *usage*
>
> *returns*
>
> *usage*
>
> *returns*
>
> Get all marks
>
> performance.getMarks()
>
> array
>
> performance.user
>
> array
>
> Get the first mark
>
> performance.getMarks()[0]
>
> mark
>
> performance.user[0]
>
> mark
>
> Get all marks named "foo"
>
> performance.getMarks("foo")
>
> array
>
> performance.user["foo"]
>
> array
>
> Get the first "foo" mark
>
> performance.getMarks("foo")[0]
>
> mark
>
> performance.user["foo"][0]
>
> mark
>
> Get all marks named "0"
>
> performance.getMarks("0")
>
> array
>
> performance.user["0"]
>
> array
>
> Get the latest "foo" mark
>
> performance.getMark("foo")
>
> mark
>
> performance.user["foo"][ performance.user["foo"].length-1]
>
> mark
>
>
>
> There can be confusion may come from the fact that if .user is indexed by a
> number, it is a single mark (the nth mark).  But if it's indexed by a
> string, it's an array of marks that match that name.
>
>
>
> The getMark()/getMarks() API [1], on the other hand, separates the
> filtering, based on the API parameters, from indexing which web developers
> can access in a standard JavaScript array returned from the API.  getMarks()
> always returns an array, which can be iterated over the standard way.  The
> getMark() interface returns the latest mark for that name and is slightly
> easier than the .user way (performance.userTiming["foo"][
> performance.userTiming["foo"].length-1]);
>

There's no table of examples to consider w/ the Object marks attribute.


>
>
> *Issue 3 – Efficiency of data structures, Requirement 3 (R3)*
>
> In terms of design efficiency data structure of having a "PerformanceMark"
> does not necessarily require that it can also be a measure.  If it's just a
> mark, it carries additional 'type' and 'measure' attributes that are not
> appropriate.  If we do add measures, we should consider splitting them into
> another object type.
>

I think we should drop measures for the same reasons we dropped them in
navigation timing.


>
>
> *Issue 4 – Naming*
>
> The attribute name ‘user’ is ambiguous.
>

Agreed. If we keep it as an attribute it should be named "marks." If it is a
method it should be "getMarks()".


>
>
> [1]
> http://dvcs.w3.org/hg/webperf/raw-file/d1498d8e0e5e/specs/UserTiming/Overview.html<https://dvcs.w3.org/hg/webperf/raw-file/d1498d8e0e5e/specs/UserTiming/Overview.html>
>
> [2] http://ie.microsoft.com/testdrive/info/downloads/Default.html
>
> [3]
> http://dvcs.w3.org/hg/webperf/raw-file/tip/specs/UserTiming/Overview.html
>
>
>
> Best Regards,
>
> Anderson, Nic and Karen
>
> Internet Explorer
>
Received on Tuesday, 1 February 2011 06:10:58 UTC

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