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Message from discussion Selecting (max) OR identity field
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SaraC  
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 More options Jun 8 2010, 11:50 am
From: SaraC <sarajchi...@gmail.com>
Date: Tue, 8 Jun 2010 08:50:00 -0700 (PDT)
Subject: Re: Selecting (max) OR identity field
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The problem is this application is a url shortener and requires an
identifier that can be hashed and
used for those purposes. I don't know of another solution while
ensuring uniqueness.

On Jun 8, 2:49 am, Ken Egozi <egoz...@gmail.com> wrote:

> select MAX is definitely wrong for the reasons mentioned.
> I would avoid Identity behaviour anyway, and not only because of the
> sharding issue. Using Identity means that every Insert must immediately call
> the database. This is not always desirable, as you might want to do more
> stuff with the Id, but postpone the DB call for later for various reasons.

> Now using the ObjectId approach has its limitations also, mainly the size
> and the readability, as some systems like human readable ids (order number,
> user id, customer service call id, etc.)
> you can enjoy both worlds if you employ the hi-lo algorithm (or
> a variation thereof). You get an integer id, generally sequential, fast to
> generate and simple to implement.

> The docs for Hibernate/NHibernate are all full with reasons to avoid
> Identity and use GuidComb (their equivalence of ObjectId) or HiLo

> On Tue, Jun 8, 2010 at 9:35 AM, Jørn Wildt <j...@fjeldgruppen.dk> wrote:
> > Check this request for some thoughts:
> >http://jira.mongodb.org/browse/SERVER-195

> > Beware of concurrency issues: two reades may read MAX() = 10 and then
> > both of them increment it to 11. You need to use MongoDB's various
> > atomic operation to ensure this operation is safe.

> > /Jørn

> > On Jun 8, 8:19 am, SaraC <sarajchi...@gmail.com> wrote:
> > > I'm new to NoSQL, I'm looking to either create an identity field (that
> > > starts at 0) or build my own by selecting a max value.

> > > I understand that the Mongo Ids are timestamps and can be used as
> > > such. However, I need a smaller value for this column.

> > > Thanks a bunch!

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> --
> Ken Egozi.http://www.kenegozi.com/bloghttp://www.delver.comhttp://www.musicglue... הכנס הקהילתי הראשון למפתחי דוטנט - בואו בהמוניכם


 
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