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

From: Keean Schupke <keean@fry-it.com>
Date: Fri, 12 Nov 2010 07:56:10 +0000
Message-ID: <AANLkTimdhx7NhC94cqeqMhCgR4MyfbsvZ-AhJ0dzkadz@mail.gmail.com>
To: Jeremy Orlow <jorlow@chromium.org>
Cc: Jonas Sicking <jonas@sicking.cc>, "Tab Atkins Jr." <jackalmage@gmail.com>, Pablo Castro <Pablo.Castro@microsoft.com>, "public-webapps@w3.org" <public-webapps@w3.org>
The other thing you could do is specify that when you get a wrap (IE someone
inserts a key of MAXINT - 1) you auto-compact the table. If you really have
run out of indexes there is not a lot you can do.

The other thing to consider it that because JS uses signed arithmetic, its
really a 63bit number... unless you want negative indexes appearing? (And
how would that affect ordering and sorting)?


Cheers,
Keean.


On 12 November 2010 07:36, Jeremy Orlow <jorlow@chromium.org> wrote:

> On Fri, Nov 12, 2010 at 10:08 AM, Jonas Sicking <jonas@sicking.cc> wrote:
>
>> 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.
>
>
> This seems reasonable.  OK, let's do it.
>
>
>> > 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 07:56:48 GMT

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