[webkit-dev] Discussing bug 98539 - Refactor resource loading to allow for out-of-process loading and memory caching

[Antti Koivisto]

On Tue, Oct 9, 2012 at 4:21 AM, Maciej Stachowiak <mjs at apple.com> wrote:

> One preliminary finding of ours is that different web pages fairly often
> load identical resource bodies from different URLs. We expect possible
> benefits from sharing the body data of resources in memory even if we
> cannot share the URL or response headers.
>

I did some preliminary profiling of this earlier. The data is not
necessarily very representative of the web as whole, I simply browsed
through a number of popular sites with an instrumented build (
https://bug-98539-attachments.webkit.org/attachment.cgi?id=167753). Here is
what I had in the WebCore memory cache in the end:

TOTAL duplicates count=443 size=852791 decodedSize=3426638
all cached resources count=2636 size=116463712

17% of cache entries are exact copies of previous entries. They use 4.3MB
out of total 116MB cache size (4%). The average size of duplicate entries
is much smaller than the average entry size (not surprisingly, transparent
1x1 images etc).

Some examples:

HTTP vs. HTTPS:

hash=5d90af size=91556 decodedSize=34834
https://ajax.googleapis.com/ajax/libs/jquery/1.6.2/jquery.min.js
hash=5d90af size=91556 decodedSize=32
http://ajax.googleapis.com/ajax/libs/jquery/1.6.2/jquery.min.js

(decodedSize for js resources is the size of the function offset cache
which can differ depending which functions have been parsed).

Ad scripts with deliberately unique URLs:

hash=6f6494 size=3111 decodedSize=32
http://ad.doubleclick.net/adj/teg.fmsq/j2ek;subs=n;wsub=n;sdn=n;dcopt=ist;pos=ldr_top;sz=728x90,970x90;tile=1;ord=76273718
?
hash=6f6494 size=3111 decodedSize=648
http://ad.doubleclick.net/adj/teg.fmsq/j2ek;subs=n;wsub=n;sdn=n;dcopt=ist;pos=ldr_top;sz=728x90,970x90;tile=1;ord=711567314
?
hash=6f6494 size=3111 decodedSize=32
http://ad.doubleclick.net/adj/teg.fmsq/j2ek;subs=n;wsub=n;sdn=n;dcopt=ist;pos=ldr_top;sz=728x90,970x90;tile=1;ord=908690779
?
hash=6f6494 size=3111 decodedSize=32
http://ad.doubleclick.net/adj/teg.fmsq/j2ek;subs=n;wsub=n;sdn=n;dcopt=ist;pos=ldr_top;sz=728x90,970x90;tile=1;ord=876087584
?

Same framework loaded by multiple unrelated sites:

hash=230c7d size=1958 decodedSize=0
http://static.iltalehti.fi/js/measure/spring.js
hash=230c7d size=1958 decodedSize=1536 http://yle.fi/global/spring/spring.js

(didn't see as many of these as expected though i'm sure there are sites
that run into this)

Copy-paste resources:

hash=8fb3e size=3965 decodedSize=13088
http://store.storeimages.cdn-apple.com/2149/store.apple.com/rs/source/store/base/nav/globalnav/css/bg/globalsearch_spinner.gif
hash=8fb3e size=3965 decodedSize=13088
http://store.storeimages.cdn-apple.com/2150/store.apple.com/rs/source/store/features/search/css/bg/spinner.gif
hash=8fb3e size=3965 decodedSize=13088
http://store.storeimages.cdn-apple.com/2150/store.apple.com/rs/source/store/base/nav/globalnav/css/bg/globalsearch_spinner.gif
hash=8fb3e size=3965 decodedSize=13088
http://images.apple.com/global/nav/images/globalsearch_spinner.gif

Versioning:

hash=cecbad size=184899 decodedSize=0
http://store.storeimages.cdn-apple.com/2150/store.apple.com/rs/applestore-rs-2.css
hash=cecbad size=184899 decodedSize=0
http://store.storeimages.cdn-apple.com/2149/store.apple.com/rs/applestore-rs-2.css

hash=47a8de size=20041 decodedSize=7870
http://js.t.sinajs.cn/open/analytics/js/suda.js?version=b4d67909ad6b5b7d
hash=47a8de size=20041 decodedSize=7870
http://tjs.sjs.sinajs.cn/open/analytics/js/suda.js

Multiple content servers:

hash=8e976b size=808 decodedSize=13088
http://i0.sinaimg.cn/home/deco/2008/0329/sinahome_0803_ws_003_new.gif
hash=8e976b size=808 decodedSize=71700
http://i3.sinaimg.cn/home/deco/2008/0329/sinahome_0803_ws_003_new.gif

Based on this I think this is definitely worth at least looking further.


  antti

You can also expect that we won't push forward blindly on this effort if
> data ultimately shows it to be a bad idea, or in general not worth the
> complexity.
>
> Regards,
> Maciej
>
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> webkit-dev mailing list
> webkit-dev at lists.webkit.org
> http://lists.webkit.org/mailman/listinfo/webkit-dev
>
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