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From Elias Levy <fearsome.lucid...@gmail.com>
Subject Re: can flink do streaming from data sources other than Kafka?
Date Thu, 07 Sep 2017 18:13:36 GMT
If you want to ensure you see all changes to a Cassandra table, you need to
make use of the Change Data Capture
<http://cassandra.apache.org/doc/latest/operating/cdc.html> feature.  For
that, you'll need code running on the Cassandra nodes to read the commit
log segments from the Cassandra CDC directory.  Given that you need to read
those files on the Cassandra nodes, and that Cassandra will stop accepting
writes to the tables if the CDC directory fills up beyond a configurable
size as a result of segments not being read, you probably don't want to
implement the segment reader within Flink.

The folks at DataMountainer have developed a Kafka Connect
<http://docs.confluent.io/current/connect/index.html> connector for Cassandra's
CDC <http://docs.datamountaineer.com/en/latest/cassandra-cdc.html>.  That
would allow you to stream Cassandra table changes out of Cassandra and into
Kafka, where they can be consumed by Flink.  The connector is part of their
stream-reactor <https://github.com/datamountaineer/stream-reactor/releases/>
repo.



On Thu, Sep 7, 2017 at 1:34 AM, kant kodali <kanth909@gmail.com> wrote:

> Yes I can indeed create them but I wonder if that is even possible? I
> haven't see any framework doing this as of today. Flink has something
> called AsyncDataStream? and I wonder if this can be leveraged to create a
> Stream out of Cassandra source?
>
> Thanks!
>
> On Thu, Sep 7, 2017 at 1:16 AM, Tzu-Li (Gordon) Tai <tzulitai@apache.org>
> wrote:
>
>> Ah, I see. I’m not aware of any existing work / JIRAs on streaming
>> sources for Cassandra or HBase, only sinks.
>> If you are interested in one, could you open JIRAs for them?
>>
>>
>> On 7 September 2017 at 4:11:05 PM, kant kodali (kanth909@gmail.com)
>> wrote:
>>
>> Hi Gordon,
>>
>> Thanks for the response, I did go over the links for sources and sinks
>> prior to posting my question. Maybe, I didn't get my question across
>> correctly so let me rephrase it. Can I get data out of data stores like
>> Cassandra, Hbase in a streaming manner? coz, currently more or less all the
>> sources are of message queue family.
>>
>> Thanks,
>> Kant
>>
>> On Thu, Sep 7, 2017 at 1:04 AM, Tzu-Li (Gordon) Tai <tzulitai@apache.org>
>> wrote:
>>
>>> Hi!
>>>
>>>
>>> I am wondering if Flink can do streaming from data sources other than
>>> Kafka. For example can Flink do streaming from a database like Cassandra,
>>> HBase, MongoDb to sinks like says Elastic search or Kafka.
>>>
>>>
>>> Yes, Flink currently supports various connectors for different sources
>>> and sinks. For an overview you can check out this documentation [1]
>>> Apache Bahir [2] also maintains some Flink connectors and is released
>>> separately.
>>>
>>> Also for out of core stateful streaming. Is RocksDB the only option?
>>>
>>> Currently, RocksDB is the only option for out-of-core state. There was
>>> some previous discussion for a Cassandra state backend, though [3].
>>>
>>> - Gordon
>>> [1] https://ci.apache.org/projects/flink/flink-docs-release-
>>> 1.3/dev/connectors/index.html
>>> [2] http://bahir.apache.org/
>>> [3] https://issues.apache.org/jira/browse/FLINK-4266
>>>
>>> On 7 September 2017 at 2:58:38 PM, kant kodali (kanth909@gmail.com)
>>> wrote:
>>>
>>> Hi All,
>>>
>>> I am wondering if Flink can do streaming from data sources other than
>>> Kafka. For example can Flink do streaming from a database like Cassandra,
>>> HBase, MongoDb to sinks like says Elastic search or Kafka.
>>>
>>> Also for out of core stateful streaming. Is RocksDB the only option? Can
>>> I use some other key value store that has SQL interface (since RocksDB
>>> doesn't)?
>>>
>>> Thanks,
>>> kant
>>>
>>>
>>
>

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