incubator-cassandra-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Ed Anuff ...@anuff.com>
Subject Re: Any way to get different unique time UUIDs for the same time value?
Date Thu, 31 Mar 2011 00:40:51 GMT
Hey Drew, I'm somewhat familiar with Snowflake, and it's certainly a
good option, but, my impression was that the main reason to use it is
because you find the 128-bits for a UUID overkill, not because it's
doing anything you can't do with UUID's.  The difference in time
resolution between UUIDs and Snowflake ids is actually greater than
the size of the sequence value that Snowflake uses to differentiate
duplicated timestamps, so the easiest thing would be just to round to
milliseconds unless your goal was to save the extra 64 bits per UUID.
I was just over-reading into Roshan's question that he wanted the full
time resolution of a UUID and on top of that be able to have a number
of duplicate timestamps.

On Wed, Mar 30, 2011 at 4:24 PM, Drew Kutcharian <drew@venarc.com> wrote:
> Hi Ed,
>
> There's no need to re-invent the wheel that's pretty much what Twitter Snowflake does.
The way it works is it creates a 64 bit long id which is formatted as such
>
> time_bits : data_center_id : machine_id : sequence
>
> Where time_bits are the milliseconds since a custom epoch.
>
> So If you see, you would get ids that are unique and ordered by time up to 1ms (if two
ids were created during the same millisecond, then the ordering is not preserved)
>
> - Drew
>
>
> On Mar 30, 2011, at 4:13 PM, Ed Anuff wrote:
>
>> If I understand the question, it's not that
>> UUIDGen.makeType1UUIDFromHost(InetAddress.getLocalHost()) is returning
>> duplicate UUID's.  It should always be giving unique time-based uuids
>> and has checks to make sure it does.  The question was whether it was
>> possible to get multiple unique time-based UUID's with the exact same
>> timestamp component, rather than avoiding duplicates in the timestamp
>> the way UUIDGen currently does.  The answer to that is that you could
>> take a look at the code for the UUIDGen class and create your own
>> version that perhaps generated the clock sequence in a different way,
>> such as leaving a certain number of low order bits of the clock
>> sequence empty and then incrementing those when duplicate timestamps
>> were generated rather than incrementing the timestamp the way UUIDGen
>> currently does.
>>
>> On Wed, Mar 30, 2011 at 10:08 AM, Drew Kutcharian <drew@venarc.com> wrote:
>>> Hi Roshan,
>>> You probably want to look at Twitter's
>>> Snowflake: https://github.com/twitter/snowflake
>>> There's also another Java variant: https://github.com/earnstone/eid
>>> - Drew
>>>
>>> On Mar 30, 2011, at 6:08 AM, Roshan Dawrani wrote:
>>>
>>> Hi,
>>> Is there any way I can get multiple unique time UUIDs for the same timestamp
>>> value - I mean, the UUIDs that are same in their time (most significant
>>> bits), but differ in their least significant bits?
>>> The least significant bits added by
>>> me.prettyprint.cassandra.utils.TimeUUIDUtils seem to be a fixed value based
>>> on mac/ip address, which makes sure that I get the same UUID for a timestamp
>>> value, everytime I ask.
>>> I need the "(timestamp): <some value>" kind of columns that need to be
>>> sorted by time, and I wanted to use TimeUUID to use column sorting that
>>> comes out-of-the-box, but the problem is that I can get multiple values for
>>> the same timestamp.
>>> So, I am looking for some way where the time portion is same, but the other
>>> UUID half is different so that I can safely store "1 time UUID: 1 value".
>>> Any help there is appreciated.
>>> --
>>> Roshan
>>> Blog: http://roshandawrani.wordpress.com/
>>> Twitter: @roshandawrani
>>> Skype: roshandawrani
>>>
>>>
>>>
>
>

Mime
View raw message