Cool, thanks for the Clarification, Kevin.
On Tue, Jun 14, 2011 at 5:43 PM, Kevin <thebachel...@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 <thebachel...@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:cassandral...@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 >
