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From Barry Wark <barryw...@gmail.com>
Subject Re: Why sequential document ids? [was: Re: What's the speed(performance) of couchdb?]
Date Fri, 27 Feb 2009 17:18:04 GMT
On Fri, Feb 27, 2009 at 8:23 AM, Paul Davis <paul.joseph.davis@gmail.com> wrote:
> On Fri, Feb 27, 2009 at 9:00 AM, Damien Katz <damien@apache.org> wrote:
>> The doc ids can be generated client side, so clients can use any scheme you
>> want. For how the server generates UUIDs, there has been some talk about
>> doing some work there, but I don't think anyone has started it.
>>
>> -Damien
>>
>>
>> On Feb 27, 2009, at 7:44 AM, Wout Mertens wrote:
>>
>>> On Feb 26, 2009, at 8:18 PM, Damien Katz wrote:
>>>>
>>>> Also, he Ids don't need to be sequential (1,2,3,4...), just ordered
>>>> (1,5,19,22...). And they don't need to sort higher or lower than all the
>>>> other ids, so long as they are clustered together.  The each btree nodes
>>>> that have to be loaded that isn't in cache is expensive. The more the keys
>>>> have to be inserted into random places in the btree, the worse the caching
>>>> behavior. Right now, with the crypto random UUIDs we generate, it's
>>>> basically the worst case scenario for doc inserts.
>>>
>>> So why not decrease security by a tunable factor and add a random number
>>> to the previous UUID instead?
>>>
>>> And while we're on the subject, I've wished for automatic doc UUIDs that
>>> nonetheless have a fixed prefix. More human readable plus it doubles as a
>>> type field... Any chance of that or is that one of the beginner mistakes?
>>>
>>> Wout.
>>
>>
>
> There was talk of switching the internal uuid generationg to a version
> 1 style instead of the version 4 (random) style. My suggestion was to
> make the _uuids endpoint accept a v=[1|4] url parameter to choose with
> a config file default but people seemed to not like that idea.
>
> HTH,
> Paul Davis
>

FWIW (though the opinions of a newbie should be taken with a big brick
of salt), I don't mind that the auto-generated UUIDs are
"conservative" in their crypto randomness. As a client, I can use
whatever scheme I want so it makes sense to go with the most
conservative default.

And thanks for the very informative answers about btrees everyone. I
learned a lot.

Cheers,
Barry

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