This still doesn’t guarantee the behavior you think it does.
From: Siddharth Verma
Reply-To: "user@cassandra.apache.org"
Date: Friday, May 6, 2016 at 12:20 AM
To: "user@cassandra.apache.org"
Subject: Re: Read data from specific node in cassandra
Hi,
Whitelist worked perfectly.
Thanks for the help.
In case, someone wants to use the same, the bellow code snippet might help them
private final Cluster mainCluster;
private final Session mainSession;
. . . . . . . . . . .
. . . . . . . . . . .
String mainHost = "IP_of_machine";
. . . . . . . . . . .
mainCluster = Cluster.builder().addContactPoint(mainHost).withQueryOptions(new
QueryOptions().setFetchSize(fetchSize)).withCredentials(username, password).
withLoadBalancingPolicy(new WhiteListPolicy(new
RoundRobinPolicy(),Arrays.asList(new InetSocketAddress(mainHost,9042))))
.build();
mainSession = mainCluster.connect();
Regards,
SIddharth Verma
On Thu, May 5, 2016 at 8:59 PM, Jeff Jirsa <jeff.ji...@crowdstrike.com> wrote:
This doesn’t actually guarantee the behavior you think it does. There’s no
actual way to guarantee this behavior in Cassandra, as far as I can tell. A
long time ago there was a ticket for a “coordinator only” consistency level,
which is nearly trivial to implement, but the use case is so narrow that it’s
unlikely to ever be done.
Here’s an example trace on system_auth, where all nodes are replicas (RF=N),
and the data is fully repaired (data exists on the local node). The coordinator
STILL chooses a replica other than itself (far more likely to see this behavior
on a keyspace with a HIGH replication factor, this particular cluster is N in
the hundreds):
cqlsh> tracing on;
Tracing is already enabled. Use TRACING OFF to disable.
cqlsh> CONSISTENCY local_one;
Consistency level set to LOCAL_ONE.
cqlsh> select name from system_auth.users where name='jjirsa' limit 1;
name
--------
jjirsa
(1 rows)
Tracing session: 5ffdee70-12d5-11e6-ad58-317180027532
activity
| timestamp | source | source_elapsed
-------------------------------------------------------------------------------------------------+----------------------------+--------------+----------------
Execute CQL3 query | 2016-05-05 15:23:52.919000 | x.y.z.150 | 0
Parsing select * from system_auth.users where name='jjirsa' limit 1;
[SharedPool-Worker-7] | 2016-05-05 15:23:52.919000 | x.y.z.150 | 100
Preparing statement
[SharedPool-Worker-7] | 2016-05-05 15:23:52.920000 | x.y.z.150 | 194
reading data from /x.y.z.151
[SharedPool-Worker-7] | 2016-05-05 15:23:52.920000 | x.y.z.150 | 965
Sending READ message to /x.y.z.151
[MessagingService-Outgoing-/x.y.z.151] | 2016-05-05 15:23:52.921000 | x.y.z.150
| 1072
REQUEST_RESPONSE message received from /x.y.z.151
[MessagingService-Incoming-/x.y.z.151] | 2016-05-05 15:23:52.924000 | x.y.z.150
| 5433
Processing response from /x.y.z.151
[SharedPool-Worker-4] | 2016-05-05 15:23:52.924000 | x.y.z.150 | 5595
READ message received from /x.y.z.150
[MessagingService-Incoming-/x.y.z.150] | 2016-05-05 15:23:52.927000 | x.y.z.151
| 104
Executing single-partition query on users
[SharedPool-Worker-6] | 2016-05-05 15:23:52.928000 | x.y.z.151 | 2251
Acquiring sstable references
[SharedPool-Worker-6] | 2016-05-05 15:23:52.929000 | x.y.z.151 | 2353
Merging memtable tombstones
[SharedPool-Worker-6] | 2016-05-05 15:23:52.929000 | x.y.z.151 | 2414
Partition index with 0 entries found for sstable 384
[SharedPool-Worker-6] | 2016-05-05 15:23:52.929000 | x.y.z.151 | 2829
Seeking to partition beginning in data file
[SharedPool-Worker-6] | 2016-05-05 15:23:52.930000 | x.y.z.151 | 2913
Skipped 0/1 non-slice-intersecting sstables, included 0 due to tombstones
[SharedPool-Worker-6] | 2016-05-05 15:23:52.930000 | x.y.z.151 | 3263
Merging data from memtables and 1 sstables
[SharedPool-Worker-6] | 2016-05-05 15:23:52.931000 | x.y.z.151 | 3289
Read 1 live and 0 tombstone cells
[SharedPool-Worker-6] | 2016-05-05 15:23:52.931000 | x.y.z.151 | 3323
Enqueuing response to /x.y.z.150
[SharedPool-Worker-6] | 2016-05-05 15:23:52.931000 | x.y.z.151 | 3411
Sending REQUEST_RESPONSE message to /x.y.z.150
[MessagingService-Outgoing-/x.y.z.150] | 2016-05-05 15:23:52.932000 | x.y.z.151
| 3577
Request complete | 2016-05-05 15:23:52.924649 | x.y.z.150 | 5649
From: Varun Barala
Reply-To: "user@cassandra.apache.org"
Date: Thursday, May 5, 2016 at 2:40 AM
To: "user@cassandra.apache.org"
Subject: Re: Read data from specific node in cassandra
Hi Siddharth Verma,
You can define consistency level LOCAL_ONE.
and you can applyh consistency level during statement creation.
like this -> statement.setConsistencyLevel(ConsistencyLevel.LOCAL_ONE);
On Thu, May 5, 2016 at 3:55 PM, Siddharth Verma <verma.siddha...@snapdeal.com>
wrote:
Hi,
We have a 3 node cluster in DC1, where replication factor of keyspace is 3.
How can i read data only from one particular node in java driver?
Thanks,
Siddharth Verma
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