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From: Valentin Kulichenko <valentin.kulichenko@gmail.com>
Date: Fri, 7 Oct 2016 13:45:46 -0700
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Subject: Re: Cassandra store questions
To: Igor Rudyak <irudyak@gmail.com>
Cc: dev@ignite.apache.org
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archived-at: Fri, 07 Oct 2016 20:46:29 -0000

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Hi Igor,

Thanks for response!

1. It's a bit inconsistent with other store implementations we have in the
product and actually I find this counterintuitive. Why don't we just load
all the data available in the table? Explicit query is useful when you want
to customize this and load subset of data based on some criteria. If this
is not possible for some reason, then I would at least throw an exception
in case query is not specified.

2. Is it possible to automatically split the data in bulks and load them in
parallel? We do this in the JDBC store, for example.

-Val

On Thu, Oct 6, 2016 at 11:00 PM, Igor Rudyak <irudyak@gmail.com> wrote:

> Hi Val,
>
> 1) If you'll call loadCache(null) it will do nothing. You need to provide
> at least one CQL query.
>
> 2) It depends. If you'll provide more than one CQL query, it will use
> separate thread for each of the queries (max number of threads limited to
> the number of CPU cores). But for each provided CQL query it will use only
> one thread to load all the data returned by the query. Also it will run the
> same CQL query from ALL Ignite nodes to load the same data, which is bad.
> That's because loadCache method will be executed on each Ignite node. As
> you see, it's not very efficient way to load data from Cassandra just by
> specifying CQL query. The ticket I created, is all about how to load data
> from one table (or from multiple tables as well) in parallel by
> partitioning it. Such a way each Ignite node will be responsible to load
> data from the specific partition range of Cassandra table, which is much
> more efficient. To support such kind of cache warm-up you should design
> your Cassandra table specific way - there should be some mapping from
> Ignite partition to the set of Cassandra partitions. Yes I have plans to
> implement this.
>
> Igor Rudyak
>
>
> On Thu, Oct 6, 2016 at 10:19 AM, Valentin Kulichenko <
> valentin.kulichenko@gmail.com> wrote:
>
>> Hi Igor,
>>
>> I've got couple of quick questions about the Cassandra store.
>>
>>    1. In [1] you suggested to provide an explicit query as a parameter
>>    for loadCache() method, because otherwise user was always getting empty
>>    result. Is this a requirement to provide the query? What if I just call
>>    loadCache(null)?
>>    2. There is a ticket [2] about parallel load in Cassandra store. Does
>>    it mean that currently it loads only in a single threaded fashion? If so,
>>    do you have any plans to implement this improvement?
>>
>> [1] http://apache-ignite-users.70518.x6.nabble.com/Cannot-
>> query-on-a-cache-using-Cassandra-as-a-persistent-store-td7870.html
>> [2] https://gridgain.freshdesk.com/helpdesk/tickets/2180
>>
>> Thanks,
>> Val
>>
>
>

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