[whatwg] Web Storage: apparent contradiction in spec
snej at google.com
Wed Aug 26 16:51:42 PDT 2009
On Aug 26, 2009, at 4:01 PM, Linus Upson wrote:
> The analogy was made comparing a user agent that purges local
> storage to an OS throwing out files without explicit user action.
> This is misleading since most files arrive on your computer's disk
> via explicit user action. You copy files to your disk by downloading
> them from the internet, copying from a network drive, from a floppy,
> your camera, etc.
A web app would also be pretty likely to put stuff in local storage as
a result of explicit user action. The use cases seem pretty similar.
Also, you're not counting files that you create locally. After all,
files have to come from somewhere :) Those are the most precious since
they're yours and they may not live anywhere else if you haven't
backed them up or copied them elsewhere. There's no reason web-apps
can't create the same kind of content, and it would look very similar
to a user: I go to the word processor [website], click New Document,
type some stuff, and click Save.
Even if the save process involves migrating the local data up to the
cloud, that transition is not instantaneous: it can take arbitrarily
large amounts of time if there are network/server problems or the user
is offline. During that time, the local storage represents the only
copy of the data. There is therefore a serious race condition where,
if the browser decides to purge local data before the app has uploaded
it, the data is gone forever.
> A better analogy would be, "What if watching TV caused 0-5MB size
> files to silently be created from time to time in a hidden folder on
> your computer, and when your disk filled up both your TV and
> computer stopped working?"
This is a cache — that isn't the kind of usage I'm concerned about.
Maybe the local storage API needs a way to distinguish between cached
data that can be silently thrown away, and important data that can't.
(For example, the Mac OS has separate 'Caches' and 'Application
Support' subfolders of ~/Library/.)
First, this is what quotas are for. The TV web-app would have a
limited quota of space to cache stuff.
Second, the browser should definitely help you delete stuff like this
if disk space does get low; I'm just saying it shouldn't delete it
silently or as part of some misleading command like "Empty Cache" or
> At a minimum the HTML 5 spec should be silent on how user agents
> implement local storage policies. I would prefer the spec to make it
> clear that local storage is a cache, domains can use up to 5MB of
> space without interrupting the user, and that UAs were free to
> implement varying cache eviction algorithms.
That will have the effect of making an interesting category of new
applications fail, with user data loss, on some browsers. That sounds
like a really bad idea to me.
To repeat what I said up above: Maybe the local storage API needs a
way to distinguish between cached data that can be silently thrown
away, and important data that can't.
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