incubator-cassandra-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Filipe Gonçalves <the.wa.syndr...@gmail.com>
Subject Re: Concurrency Control
Date Wed, 30 May 2012 09:44:11 GMT
It's the timestamps provided in the columns that do concurrency
control/conflict resolution. Basically, the newer timestamp wins.
For counters I think there is no such mechanism (i.e. counter updates are
not idempotent).

>From https://wiki.apache.org/cassandra/DataModel :

All values are supplied by the client, including the 'timestamp'. This
> means that clocks on the clients should be synchronized (in the Cassandra
> server environment is useful also), as these timestamps are used for
> conflict resolution. In many cases the 'timestamp' is not used in client
> applications, and it becomes convenient to think of a column as a
> name/value pair. For the remainder of this document, 'timestamps' will be
> elided for readability. It is also worth noting the name and value are
> binary values, although in many applications they are UTF8 serialized
> strings.
> Timestamps can be anything you like, but microseconds since 1970 is a
> convention. Whatever you use, it must be consistent across the application,
> otherwise earlier changes may overwrite newer ones.


2012/5/28 Helen <live42day@gmx.ch>

> Hi,
> what kind of Concurrency Control Method is used in Cassandra? I found out
> so far
> that it's not done with the MVCC Method and that no vector clocks are
> being used.
> Thanks Helen
>
>


-- 
Filipe Gonçalves

Mime
View raw message