[webkit-dev] Existing metrics for deprecated features

Pavel Feldman pfeldman at chromium.org
Thu Sep 13 22:58:49 PDT 2012

On Fri, Sep 14, 2012 at 4:13 AM, Adam Barth <abarth at webkit.org> wrote:

> In connection with the thread on webkitPostMessage, I took a look at
> what sorts of metrics we have currently for depreciated features.  We
> have high quality data for two groups of APIs:
> For mutation events, we measure what percent of Documents have
> listeners for various kinds of mutation events:
> DOMAPI.PerDocumentMutationEventUsage.DOMCharacterDataModified: 2.85%
> of all Documents
> DOMAPI.PerDocumentMutationEventUsage.DOMNodeInserted: 4.78% of all
> Documents
> DOMAPI.PerDocumentMutationEventUsage.DOMNodeInsertedIntoDocument:
> 0.21% of all Documents
> DOMAPI.PerDocumentMutationEventUsage.DOMNodeRemoved: 0.07% of all Documents
> DOMAPI.PerDocumentMutationEventUsage.DOMNodeRemovedFromDocument:
> 0.0003% of all Documents
> DOMAPI.PerDocumentMutationEventUsage.DOMSubtreeModified: 2.30% of all
> Documents
> From this data, it's tempting to remove support for DOMNodeRemoved and
> DOMNodeRemovedFromDocument as those are used extremely rarely.  We
> don't have any data for how much of this usage is attributable to
> extensions.  It will be interesting to watch this data as we
> evangelize MutationObservers, especially among extension developers.

Is there an absolute number for those 0.07%? How is it calculated? Like Web
Inspector has been using DOMNodeRemoved for its viewport-based text editor
until very recently, so your 0.07% is likely to include millions of users.
Is that expected? I wonder what will the drop be with the next major Chrome

> Another metric we have is for Blob.webkitSlice:
> Ratio of Blob.webkitSlice calls to Blob.slice: 14.87%
> Ratio of Blob.webkitSlice calls to Document creation: 0.0053%
> It's difficult to know how to interpret this data because we don't
> actually correlate calls to webkitSlice with Documents or Pages.
> Instead, we just count the total number of calls across all Documents.
>  This gives us an upper bound on how many Documents (or Pages) would
> be affected by deleting Blob.webkitSlice, but doesn't measure that
> information as accurately as the data we have for mutation events.
> We are also gathering metrics on the usage of vendor prefixes in CSS
> properties, but that histogram doesn't appear to have been in the
> field long enough to have meaningful data.
> Adam
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