Re: cqlinputformat and retired cqlpagingingputformat creates lots of connections to query the server
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
Re: cqlinputformat and retired cqlpagingingputformat creates lots of connections to query the server
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
Re: cqlinputformat and retired cqlpagingingputformat creates lots of connections to query the server
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
Re: cqlinputformat and retired cqlpagingingputformat creates lots of connections to query the server
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
Re: cqlinputformat and retired cqlpagingingputformat creates lots of connections to query the server
I mean when the number of nodes grow, there are more virtual nodes in total. For each vnode (or a partition range), a connection will be created. For 3 node, 256 tokens each, replication factor=1 for simplicity, there will be 3*256 virtual nodes, and therefore that many connections. Let me know if there is any incorrect reasoning here. Thanks. On Tue, Jan 27, 2015 at 11:21 PM, Huiliang Zhang zhl...@gmail.com wrote: In that case, each node will have 256/3 connections at most. Still 256 mappers. Someone please correct me if I am wrong. On Tue, Jan 27, 2015 at 11:04 PM, Shenghua(Daniel) Wan wansheng...@gmail.com wrote: Hi, Huiliang, Great to hear from you, again! Image you have 3 nodes, replication factor=1, and using default number of tokens. You will have 3*256 mappers... In that case, you will be soon out of mappers or reach the limit. On Tue, Jan 27, 2015 at 10:59 PM, Huiliang Zhang zhl...@gmail.com wrote: Hi Shenghua, as I understand, each range is assigned to a mapper. Mapper will not share connections. So, it needs at least 256 connections to read all. But all 256 connections should not be set up at the same time unless you have 256 mappers running at the same time. On Tue, Jan 27, 2015 at 9:34 PM, Shenghua(Daniel) Wan wansheng...@gmail.com wrote: By default, each C* node is set with 256 tokens. On a local 1-node C* server, my hadoop drop creates 256 connections to the server. Is there any way to control this behavior? e.g. reduce the number of connections to a pre-configured gap. I debugged C* source code and found the client asks for partition ranges, or virtual nodes. Then the client was told by server there were 257 ranges, corresponding to 257 column family splits. Here is a snapshot of my logs 15/01/27 18:02:20 DEBUG hadoop.AbstractColumnFamilyInputFormat: adding ColumnFamilySplit((9121856086738887846, '-9223372036854775808] @[localhost]) ... totally 257 splits. 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? My C* version is 2.0.11 and I also tried CqlPagingInputFormat, which has same behavior. Thank you. -- Regards, Shenghua (Daniel) Wan -- Regards, Shenghua (Daniel) Wan -- Regards, Shenghua (Daniel) Wan
Re: cqlinputformat and retired cqlpagingingputformat creates lots of connections to query the server
Hi, Huiliang, Great to hear from you, again! Image you have 3 nodes, replication factor=1, and using default number of tokens. You will have 3*256 mappers... In that case, you will be soon out of mappers or reach the limit. On Tue, Jan 27, 2015 at 10:59 PM, Huiliang Zhang zhl...@gmail.com wrote: Hi Shenghua, as I understand, each range is assigned to a mapper. Mapper will not share connections. So, it needs at least 256 connections to read all. But all 256 connections should not be set up at the same time unless you have 256 mappers running at the same time. On Tue, Jan 27, 2015 at 9:34 PM, Shenghua(Daniel) Wan wansheng...@gmail.com wrote: By default, each C* node is set with 256 tokens. On a local 1-node C* server, my hadoop drop creates 256 connections to the server. Is there any way to control this behavior? e.g. reduce the number of connections to a pre-configured gap. I debugged C* source code and found the client asks for partition ranges, or virtual nodes. Then the client was told by server there were 257 ranges, corresponding to 257 column family splits. Here is a snapshot of my logs 15/01/27 18:02:20 DEBUG hadoop.AbstractColumnFamilyInputFormat: adding ColumnFamilySplit((9121856086738887846, '-9223372036854775808] @[localhost]) ... totally 257 splits. 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? My C* version is 2.0.11 and I also tried CqlPagingInputFormat, which has same behavior. Thank you. -- Regards, Shenghua (Daniel) Wan -- Regards, Shenghua (Daniel) Wan
Re: cqlinputformat and retired cqlpagingingputformat creates lots of connections to query the server
In that case, each node will have 256/3 connections at most. Still 256 mappers. Someone please correct me if I am wrong. On Tue, Jan 27, 2015 at 11:04 PM, Shenghua(Daniel) Wan wansheng...@gmail.com wrote: Hi, Huiliang, Great to hear from you, again! Image you have 3 nodes, replication factor=1, and using default number of tokens. You will have 3*256 mappers... In that case, you will be soon out of mappers or reach the limit. On Tue, Jan 27, 2015 at 10:59 PM, Huiliang Zhang zhl...@gmail.com wrote: Hi Shenghua, as I understand, each range is assigned to a mapper. Mapper will not share connections. So, it needs at least 256 connections to read all. But all 256 connections should not be set up at the same time unless you have 256 mappers running at the same time. On Tue, Jan 27, 2015 at 9:34 PM, Shenghua(Daniel) Wan wansheng...@gmail.com wrote: By default, each C* node is set with 256 tokens. On a local 1-node C* server, my hadoop drop creates 256 connections to the server. Is there any way to control this behavior? e.g. reduce the number of connections to a pre-configured gap. I debugged C* source code and found the client asks for partition ranges, or virtual nodes. Then the client was told by server there were 257 ranges, corresponding to 257 column family splits. Here is a snapshot of my logs 15/01/27 18:02:20 DEBUG hadoop.AbstractColumnFamilyInputFormat: adding ColumnFamilySplit((9121856086738887846, '-9223372036854775808] @[localhost]) ... totally 257 splits. 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? My C* version is 2.0.11 and I also tried CqlPagingInputFormat, which has same behavior. Thank you. -- Regards, Shenghua (Daniel) Wan -- Regards, Shenghua (Daniel) Wan
Re: cqlinputformat and retired cqlpagingingputformat creates lots of connections to query the server
For clarification, please checkout the source code I got from C* v2.0.11
in AbstractColumnFamilyInputFormat getSplits(JobContext context)
line 125 and 168
// cannonical ranges and nodes holding replicas
ListTokenRange masterRangeNodes = getRangeMap(conf);
for (TokenRange range : masterRangeNodes)
{
if (jobRange == null)
{
// for each range, pick a live owner and ask it to
compute bite-sized splits
splitfutures.add(executor.submit(new
SplitCallable(range, conf)));
}
My understanding for this part of source code is for each token range, it
will create a connection to the server.
On Tue, Jan 27, 2015 at 11:21 PM, Huiliang Zhang zhl...@gmail.com wrote:
In that case, each node will have 256/3 connections at most. Still 256
mappers. Someone please correct me if I am wrong.
On Tue, Jan 27, 2015 at 11:04 PM, Shenghua(Daniel) Wan
wansheng...@gmail.com wrote:
Hi, Huiliang,
Great to hear from you, again!
Image you have 3 nodes, replication factor=1, and using default number of
tokens. You will have 3*256 mappers... In that case, you will be soon out
of mappers or reach the limit.
On Tue, Jan 27, 2015 at 10:59 PM, Huiliang Zhang zhl...@gmail.com
wrote:
Hi Shenghua, as I understand, each range is assigned to a mapper. Mapper
will not share connections. So, it needs at least 256 connections to read
all. But all 256 connections should not be set up at the same time unless
you have 256 mappers running at the same time.
On Tue, Jan 27, 2015 at 9:34 PM, Shenghua(Daniel) Wan
wansheng...@gmail.com wrote:
By default, each C* node is set with 256 tokens. On a local 1-node C*
server, my hadoop drop creates 256 connections to the server. Is there any
way to control this behavior? e.g. reduce the number of connections to a
pre-configured gap.
I debugged C* source code and found the client asks for partition
ranges, or virtual nodes. Then the client was told by server there were 257
ranges, corresponding to 257 column family splits.
Here is a snapshot of my logs
15/01/27 18:02:20 DEBUG hadoop.AbstractColumnFamilyInputFormat: adding
ColumnFamilySplit((9121856086738887846, '-9223372036854775808]
@[localhost])
...
totally 257 splits.
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?
My C* version is 2.0.11 and I also tried CqlPagingInputFormat, which
has same behavior.
Thank you.
--
Regards,
Shenghua (Daniel) Wan
--
Regards,
Shenghua (Daniel) Wan
--
Regards,
Shenghua (Daniel) Wan
cqlinputformat and retired cqlpagingingputformat creates lots of connections to query the server
By default, each C* node is set with 256 tokens. On a local 1-node C* server, my hadoop drop creates 256 connections to the server. Is there any way to control this behavior? e.g. reduce the number of connections to a pre-configured gap. I debugged C* source code and found the client asks for partition ranges, or virtual nodes. Then the client was told by server there were 257 ranges, corresponding to 257 column family splits. Here is a snapshot of my logs 15/01/27 18:02:20 DEBUG hadoop.AbstractColumnFamilyInputFormat: adding ColumnFamilySplit((9121856086738887846, '-9223372036854775808] @[localhost]) ... totally 257 splits. 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? My C* version is 2.0.11 and I also tried CqlPagingInputFormat, which has same behavior. Thank you. -- Regards, Shenghua (Daniel) Wan
