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From DuyHai Doan <doanduy...@gmail.com>
Subject Re: full-tabe scan - extracting all data from C*
Date Wed, 28 Jan 2015 16:30:49 GMT
Hint: using the Java driver, you can set the fetchSize to tell the driver
how many CQL rows to fetch for each page.

 Depending on the size (in bytes) of each CQL row, it would be useful to
tune this fetchSize value to avoid loading too much data into memory for
each page

On Wed, Jan 28, 2015 at 8:20 AM, Xu Zhongxing <xu_zhong_xing@163.com> wrote:

> This is hard to answer. The performance is a thing depending on context.
> You could tune various parameters.
>
> At 2015-01-28 14:43:38, "Shenghua(Daniel) Wan" <wanshenghua@gmail.com>
> wrote:
>
> Cool. What about performance? e.g. how many record for how long?
>
> On Tue, Jan 27, 2015 at 10:16 PM, Xu Zhongxing <xu_zhong_xing@163.com>
> wrote:
>
>> For Java driver, there is no special API actually, just
>>
>> ResultSet rs = session.execute("select * from ...");
>> for (Row r : rs) {
>>    ...
>> }
>>
>> For Spark, the code skeleton is:
>>
>> val rdd = sc.cassandraTable("ks", "table")
>>
>> then call various standard Spark API to process the table parallelly.
>>
>> I have not used CqlInputFormat.
>>
>> At 2015-01-28 13:38:20, "Shenghua(Daniel) Wan" <wanshenghua@gmail.com>
>> wrote:
>>
>> Hi, Zhongxing,
>> I am also interested in your table size. I am trying to dump 10s Million
>> record data from C* using map-reduce related API like CqlInputFormat.
>> You mentioned about Java driver. Could you suggest any API you used?
>> Thanks.
>>
>> On Tue, Jan 27, 2015 at 5:33 PM, Xu Zhongxing <xu_zhong_xing@163.com>
>> wrote:
>>
>>> Both Java driver "select * from table" and Spark sc.cassandraTable()
>>> work well.
>>> I use both of them frequently.
>>>
>>> At 2015-01-28 04:06:20, "Mohammed Guller" <mohammed@glassbeam.com>
>>> wrote:
>>>
>>>  Hi –
>>>
>>>
>>>
>>> Over the last few weeks, I have seen several emails on this mailing list
>>> from people trying to extract all data from C*, so that they can import
>>> that data into other analytical tools that provide much richer analytics
>>> functionality than C*. Extracting all data from C* is a full-table scan,
>>> which is not the ideal use case for C*. However, people don’t have much
>>> choice if they want to do ad-hoc analytics on the data in C*.
>>> Unfortunately, I don’t think C* comes with any built-in tools that make
>>> this task easy for a large dataset. Please correct me if I am wrong. Cqlsh
>>> has a COPY TO command, but it doesn’t really work if you have a large
>>> amount of data in C*.
>>>
>>>
>>>
>>> I am aware of couple of approaches for extracting all data from a table
>>> in C*:
>>>
>>> 1)      Iterate through all the C* partitions (physical rows) using the
>>> Java Driver and CQL.
>>>
>>> 2)      Extract the data directly from SSTables files.
>>>
>>>
>>>
>>> Either approach can be used with Hadoop or Spark to speed up the
>>> extraction process.
>>>
>>>
>>>
>>> I wanted to do a quick survey and find out how many people on this
>>> mailing list have successfully used approach #1 or #2 for extracting large
>>> datasets (terabytes) from C*. Also, if you have used some other techniques,
>>> it would be great if you could share your approach with the group.
>>>
>>>
>>>
>>> Mohammed
>>>
>>>
>>>
>>>
>>
>>
>> --
>>
>> Regards,
>> Shenghua (Daniel) Wan
>>
>>
>
>
> --
>
> Regards,
> Shenghua (Daniel) Wan
>
>

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