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From "Wangpei (Peter)" <peter.wang...@huawei.com>
Subject Re: Basic question on a write operation immediately followed by a read
Date Tue, 25 Jan 2011 07:23:38 GMT
What is the ConsistencyLevel value? Is it ConsistencyLevel.ANY?

Javadoc:
* Write consistency levels make the following guarantees before reporting success to the client:
*   ANY          Ensure that the write has been written once somewhere, including possibly
being hinted in a non-target node.
*   ONE          Ensure that the write has been written to at least 1 node's commit log and
memory table
*   QUORUM       Ensure that the write has been written to <ReplicationFactor> / 2 +
1 nodes
*   LOCAL_QUORUM Ensure that the write has been written to <ReplicationFactor> / 2 +
1 nodes, within the local datacenter (requires NetworkTopologyStrategy)
*   EACH_QUORUM  Ensure that the write has been written to <ReplicationFactor> / 2 +
1 nodes in each datacenter (requires NetworkTopologyStrategy)
*   ALL          Ensure that the write is written to <code>&lt;ReplicationFactor&gt;</code>
nodes before responding to the client.



发件人: Roshan Dawrani [mailto:roshandawrani@gmail.com]
发送时间: 2011年1月25日 10:57
收件人: user@cassandra.apache.org; hector-users@googlegroups.com
主题: Basic question on a write operation immediately followed by a read

Hi,

I have a basic question - maybe silly too.

Say, I have a 1-node Cassandra setup (no replication, eventual consistency, etc) and I do
an insert into a column family and then very close in time to the insert, I do a read on it
for the same data.

Is there a possibility that my read operation may miss the data that just got inserted?

Since there are no DB transactions in Cassandra, are writes immediately seen to readers -
even partially as they get written?

Or can there be a delay sometimes due to flusing-to-SSTables, etc?

Or, the writes are first in-memory and immediately visible to readers and flusing, etc is
independent of all this and happens in background?
Thanks.

--
Roshan
Blog: http://roshandawrani.wordpress.com/
Twitter: @roshandawrani<http://twitter.com/roshandawrani>
Skype: roshandawrani
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