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From Sameer Farooqui <cassandral...@gmail.com>
Subject Re: When does it make sense to use TimeUUID?
Date Wed, 15 Jun 2011 00:52:09 GMT
Cool, thanks for the Clarification, Kevin.


On Tue, Jun 14, 2011 at 5:43 PM, Kevin <thebachellor@gmail.com> wrote:

> Correction. TimeUUID comparisons FIRST compare the  time-based portion,
> then go on to the other portion.
>
>
>

On Tue, Jun 14, 2011 at 5:41 PM, Kevin <thebachellor@gmail.com> wrote:

> TimeUUIDs should be used for data that is time-based and requires
> uniqueness.
>
>
>
> TimeUUID comparisons compare the time-based portion of the UUID. So no, you
> do not need to know the MAC addresses. In fact, for languages that cannot
> get to that low of a level to access a MAC address (like Java), the timeUUID
> tools generate random data for that part of the UUID.
>
>
>
> I don’t understand your “user1”/”user2” scenario. The timeUUIDs in that
> scenario wouldn’t even come in to question because the columns would be in
> two different rows since they pertain to two different users (unless they
> are referencing some other Column Family where those same TimeUUIDs are rows
> or columns in the same row).
>
>
>
> A good example of something that timeUUIDs would be great for would be
> friend requests. Regular time-based strings would not be sufficient in this
> case since it’s possible that two requests can be sent from two different
> computers at the same time. Thus, you can store the requests as columns (or
> super columns) each named by a timeUUID. Later (assuming you’ve chosen to
> let Cassandra sort the columns or supercolumns by timeUUID), you can fetch
> all the requests for a given user in either most-recent, or least-recent
> order.
>
> *From:* Sameer Farooqui [mailto:cassandralabs@gmail.com]
> *Sent:* Tuesday, June 14, 2011 8:16 PM
>
> *To:* user@cassandra.apache.org
> *Subject:* When does it make sense to use TimeUUID?
>
>
>
> I would like to store some timestamped user info in a Column Family with
> the usernames as the row key and different timestamps as column names. Each
> user might have a thousand timestamped data.
>
>
>
> I understand that the ver 1 UUIDs that Cassandra combines the MAC address
> of the computer generating the UUID with the number of 100-nanosecond
> intervals since the beginning of the Gregorian calendar.
>
>
>
> So, if user1 had data stored for an event at Jan 30, 2011/2:15pm and user2
> had an event at the exact same time, the data could potentially be stored in
> different column names? So, I would have to know the MAC of the generating
> computer in order to do a column slice, right?
>
>
>
> When does it make sense to use TimeUUID vs just a time string like
> 20110130141500 and comparator type UTF8?
>
>
>
> - Sameer
>

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