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From Даниел Симеонов <dsimeo...@gmail.com>
Subject questions about consistency
Date Wed, 21 Apr 2010 07:46:03 GMT
Hello,
   I am pretty new to Cassandra and I have some questions, they may seem
trivial, but still I am pretty new to the subject. First is about the lack
of a compareAndSet() operation, as I understood it is not supported
currently in Cassandra, do you know of use cases which really require such
operations and how these use cases currently workaround this .
Second topic I'd like to discuss a little bit more is about the read repair,
as I understand is that it is being done by the timestamps supplied by the
client application servers. Since computer clocks (which requires
synchronization algorithms working regularly) diverge there should be a time
frame during which the order of the client request written to the database
is not guaranteed, do you have real world experiences with this? Is this
similar to the casual consistency (
http://en.wikipedia.org/wiki/Causal_consistency ) .What happens if two
application servers try to update the same data and supply one and the same
timestamp (it could happen although rarely), what if they try to update
several columns in batch operation this way, is there a chance that the
column value could be intermixed between the two update requests?
I have one last question about the consistency level ALL, do you know of
real use cases where it is required (instead of QUORUM) and why (both read
and write)?
Thank you very much for your help to better understand 'Cassandra'!
Best regards, Daniel.

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