That's c* default setting. My version is 2.0.11. Check your Cassandra.yaml. On Jan 28, 2015 4:53 PM, "Huiliang Zhang" <zhl...@gmail.com> wrote:
> If you are using replication factor 1 and 3 cassandra nodes, 256 virtual > nodes should be evenly distributed on 3 nodes. So there are totally 256 > virtual nodes. But in your experiment, you saw 3*257 mapper. Is that > because of the setting cassandra.input.split.size=3? It is nothing with > node number=3. Otherwise, I am confused why there are 256 virtual nodes on > every cassandra node. > > On Wed, Jan 28, 2015 at 12:29 AM, Shenghua(Daniel) Wan < > wansheng...@gmail.com> wrote: > >> I did another experiment to verify indeed 3*257 (1 of 257 ranges is null >> effectively) mappers were created. >> >> Thanks mcm for the information ! >> >> On Wed, Jan 28, 2015 at 12:17 AM, mck <m...@apache.org> wrote: >> >>> Shenghua, >>> >>> > The problem is the user might only want all the data via a "select *" >>> > like statement. It seems that 257 connections to query the rows are >>> necessary. >>> > However, is there any way to prohibit 257 concurrent connections? >>> >>> >>> Your reasoning is correct. >>> The number of connections should be tunable via the >>> "cassandra.input.split.size" property. See >>> ConfigHelper.setInputSplitSize(..) >>> >>> The problem is that vnodes completely trashes this, since splits >>> returned don't span across vnodes. >>> There's an issue out for this – >>> https://issues.apache.org/jira/browse/CASSANDRA-6091 >>> but part of the problem is that the thrift stuff involved here is >>> getting rewritten¹ to be pure cql. >>> >>> In the meantime you override the CqlInputFormat and manually re-merge >>> splits together, where location sets match, so to better honour >>> inputSplitSize and to return to a more reasonable number of connections. >>> We do this, using code similar to this patch >>> https://github.com/michaelsembwever/cassandra/pull/2/files >>> >>> ~mck >>> >>> ¹ https://issues.apache.org/jira/browse/CASSANDRA-8358 >>> >> >> >> >> -- >> >> Regards, >> Shenghua (Daniel) Wan >> > >
