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Re: [Bug 11270] New: Interaction between in-line keys and key generators

From: Jonas Sicking <jonas@sicking.cc>
Date: Thu, 11 Nov 2010 23:08:58 -0800
Message-ID: <AANLkTik5eG3HcgBRQUw9vaX4HoTzUwd_u7F+4p02hy5i@mail.gmail.com>
To: Jeremy Orlow <jorlow@chromium.org>
Cc: "Tab Atkins Jr." <jackalmage@gmail.com>, Pablo Castro <Pablo.Castro@microsoft.com>, "public-webapps@w3.org" <public-webapps@w3.org>
On Thu, Nov 11, 2010 at 9:22 PM, Jeremy Orlow <jorlow@chromium.org> wrote:
> On Fri, Nov 12, 2010 at 12:32 AM, Jonas Sicking <jonas@sicking.cc> wrote:
>>
>> On Thu, Nov 11, 2010 at 11:41 AM, Jeremy Orlow <jorlow@chromium.org>
>> wrote:
>> > On Thu, Nov 11, 2010 at 6:41 PM, Tab Atkins Jr. <jackalmage@gmail.com>
>> > wrote:
>> >>
>> >> On Thu, Nov 11, 2010 at 4:20 AM, Jeremy Orlow <jorlow@chromium.org>
>> >> wrote:
>> >> > What would we do if what they provided was not an integer?
>> >>
>> >> The behavior isn't very important; throwing would be fine here.  In
>> >> mySQL, you can only put AUTO_INCREMENT on columns in the integer
>> >> family.
>> >>
>> >>
>> >> > What happens if
>> >> > the number they insert is so big that the next one causes overflow?
>> >>
>> >> The same thing that happens if you do ++ on a variable holding a
>> >> number that's too large.  Or, more directly, the same thing that
>> >> happens if you somehow fill up a table to the integer limit (probably
>> >> deleting rows along the way to free up space), and then try to add a
>> >> new row.
>> >>
>> >>
>> >> > What is
>> >> > the use case for this?  Do we really think that most of the time
>> >> > users
>> >> > do
>> >> > this it'll be intentional and not just a mistake?
>> >>
>> >> A big one is importing some data into a live table.  Many smaller ones
>> >> are related to implicit data constraints that exist in the application
>> >> but aren't directly expressed in the table.  I've had several times
>> >> when I could normally just rely on auto-numbering for something, but
>> >> occasionally, due to other data I was inserting elsewhere, had to
>> >> specify a particular id.
>> >
>> > This assumes that your autonumbers aren't going to overlap and is going
>> > to
>> > behave really badly when they do.
>> > Honestly, I don't care too much about this, but I'm skeptical we're
>> > doing
>> > the right thing here.
>>
>> Pablo did bring up a good use case, which is wanting to migrate
>> existing data to a new object store, for example with a new schema.
>> And every database examined so far has some ability to specify
>> autonumbered columns.
>>
>> overlaps aren't a problem in practice since 64bit integers are really
>> really big. So unless someone "maliciously" sets a number close to the
>> upper bound of that then overlaps won't be a problem.
>
> Yes, but we'd need to spec this, implement it, and test it because someone
> will try to do this maliciously.

I'd say it's fine to treat the range of IDs as a hardware limitation.
I.e. similarly to how we don't specify how much data a webpage is
allowed to put into DOMStrings, at some point every implementation is
going to run out of memory and effectively limit it. In practice this
isn't a problem since the limit is high enough.

Another would be to define that the ID is 64 bit and if you run out of
IDs no more rows can be inserted into the objectStore. At that point
the page is responsible for creating a new object store and compacting
down IDs. In practice no page will run into this limitation if they
use IDs increasing by one. Even if you generate a new ID a million
times a second, it'll still take you over half a million years to run
out of 64bit IDs.

> And, in the email you replied right under, I brought up the point that this
> feature won't help someone who's trying to import data into a table that
> already has data in it because some of it might clash.  So, just to make
> sure we're all on the same page, the use case for this is restoring data
> into an _empty_ object store, right?  (Because I don't think this is a good
> solution for much else.)

That's the main scenario I can think of that would require this yes.

/ Jonas
Received on Friday, 12 November 2010 07:09:56 GMT

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