[webkit-dev] localStorage quota limit

Jeremy Orlow jorlow at chromium.org
Wed Dec 2 10:48:15 PST 2009

+ hixie

I don't know as much about encoding types as I should.  How can you
construct invalid UTF-16 sequences?  What does Firefox or IE do with these
when put into LocalStorage?

One thing I just considered is that our LocalStorage implementation loads
the entire LocalStorage database for an origin into memory all at once.  It
does this on a background thread, but it's only loaded on the first access
to |window.localStorage| and we block on it finishing loading when you first
try to use it.  So if |alert(window.localStorage.foo);| is the first usage
of LocalStorage, it (and thus the main thread) will block on the whole thing
being loaded into memory.  This can certainly be optimized, but I'm pointing
this out because the bigger the DB is, the worse the worst case load time
is.  (Making this better is on my todo list, but not as near the top as I'd

In case you're wondring, you can mitigate this by doing 'var storage =
window.localStorage;' as early as possible in your script and waiting as
long as possible to actually use window.localStorage.


On Wed, Dec 2, 2009 at 10:01 AM, Darin Adler <darin at apple.com> wrote:

> On Dec 2, 2009, at 9:49 AM, Darin Fisher wrote:
> > This would probably be a performance win since it would reduce the amount
> of disk i/o.
> >
> > (Note, it doesn't mean that 5 million characters could be stored since a
> UTF-8 character might be multi-byte.)
> Currently the database can store invalid UTF-16 as well as valid UTF-16.
> Conversion from UTF-16 to UTF-8 might not be able to preserve invalid UTF-16
> sequences. I don’t understand how the other platforms handle this. Perhaps
> the specification needs to be clearer on whether invalid UTF-16 is allowed.
>    -- Darin
> _______________________________________________
> webkit-dev mailing list
> webkit-dev at lists.webkit.org
> http://lists.webkit.org/mailman/listinfo.cgi/webkit-dev
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