To Sir Oleksandr :
Thank you very much for your careful teaching, at the begging, I copied
system_auth keyspace and tables' sql grammar
and misunderstood the HA function of cassandra, now I know cassandra'ha as
hadoop or greenplum.
And I will check the 3rd answer on Jconsole latter.
On the 2nd question, would you like to tell me how to change a write's
and a read's consistency level separately in cqlsh?
Otherwise, how the document's R+W>Replicator to realize to guarantee a strong
consistency write and read?
Thank you!
Sincerely
Nimbuslin(Lin JiaXin)
Mobile: 0086 180 5986 1565
Mail: [email protected]
________________________________________
From: Oleksandr Shulgin <[email protected]>
Sent: Monday, June 17, 2019 7:19 AM
To: User
Subject: Re: How can I check cassandra cluster has a real working function of
high availability?
On Sat, Jun 15, 2019 at 4:31 PM Nimbus Lin
<[email protected]<mailto:[email protected]>> wrote:
Dear cassandra's pioneers:
I am a 5 years' newbie, it is until now that I have time to use cassandra.
but I cann't check cassandra's high availabily when I stop a seed node or none
seed DN as CGE or Greenplum.
Would someone can tell me how to check the cassandra's high availability?
even I change the consistency level from one to local_one, the cqlsh's select
is always return an error of NoHostAvailable.
By the way, would you like to answer me other two questions:
2nd question: although cassandrfa's consistency is a per-operation setting,
isn't there a whole all operations' consistency setting method?
3rd question: how can I can cassandra cluster's running variables as mysql's
show global variables? such as hidden variable of auto_bootstrap?
Hi,
For the purpose of serving client requests, all nodes are equal -- seed or not.
So it shouldn't matter which node you are stopping (or making it unavailable
for the rest of the cluster using other means).
In order to test it with cqlsh you should ensure that the replication factors
of the keyspace you're testing with is sufficient. Given the NoHostAvailable
exception that you are experiencing at consistency level ONE (or LOCAL_ONE), I
can guess that you are testing with a keyspace with replication factor 1 and
the node which is unavailable happen to be responsible for the particular
partition.
For your second question: it depends on a client (or "client driver") you are
using. In cqlsh you can set consistency level that will be applied for all
subsequent queries using the "CONSISTENCY ..." command. I think that the Java
driver does have an option to set the default consistency level, as well as has
an option to set consistency level per query. Most likely this is also true
for Python and other drivers.
And for the third question: I'm not aware of a CQL or nodetool command that
would fulfill the need. Most likely it is possible to learn (and update) most
of the configuration parameters using JMX, e.g. with JConsole:
https://docs.datastax.com/en/archived/cassandra/3.0/cassandra/operations/opsMonitoring.html#opsMonitoringJconsole
Cheers,
--
Alex
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