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From Valentin Kulichenko <valentin.kuliche...@gmail.com>
Subject Re: Cassandra store questions
Date Thu, 13 Oct 2016 23:37:15 GMT
Here is the ticket: https://issues.apache.org/jira/browse/IGNITE-4075

-Val

On Wed, Oct 12, 2016 at 6:45 PM, Igor Rudyak <irudyak@gmail.com> wrote:

> Hi Val,
>
> I don't have any objections - please create a ticket and link it to the
> root ticket https://issues.apache.org/jira/browse/IGNITE-1371
>
> Igor
>
> On Wed, Oct 12, 2016 at 4:10 PM, Valentin Kulichenko <
> valentin.kulichenko@gmail.com> wrote:
>
>> Hi Igor,
>>
>> 1. I still think we should do this. Loading nothing is very
>> counterintuitive and prevents a newbie user from quick start. For large
>> tables, when only part of the dataset is needed, user will explicitly
>> specify the query, of course. Do you have objections? If no, I will create
>> a ticket.
>>
>> 2. Got it, thanks.
>>
>> -Val
>>
>> On Mon, Oct 10, 2016 at 12:12 AM, Igor Rudyak <irudyak@gmail.com> wrote:
>>
>>> Hi Val,
>>>
>>> 1) Well, it's not a problem to implement such default behavior, but
>>> there is one concern. In most cases, when you are using Cassandra as a
>>> persistent store you are going to store large amount of data, which is
>>> significantly bigger that amount of RAM in your Ignite cluster. In the such
>>> case it doesn't make sense to launch CQL query like "select * from
>>> my_table" cause:
>>>    a) You still will not be able to keep all data from Cassandra table
>>> in Ignite cache
>>>    b) All the data will be pulled from Cassandra table using only one
>>> thread - which is very slow
>>>
>>> 2) Unfortunately it's not possible in Cassandra. For JDBC you are
>>> splitting table into chunks of 512 rows each, using sub-queries and
>>> ordering by primary keys. Such kind of things are not supported in
>>> Cassandra. Probably the only way to load data from Cassandra table in
>>> parallel, is to load it from some specified partitions (in parallel for
>>> each partition).
>>>
>>>
>>> Igor Rudyak
>>>
>>> On Fri, Oct 7, 2016 at 1:45 PM, Valentin Kulichenko <
>>> valentin.kulichenko@gmail.com> wrote:
>>>
>>>> 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-qu
>>>>>> ery-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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