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From Robin Verlangen <ro...@us2.nl>
Subject Re: Why Cassandra secondary indexes are so slow on just 350k rows?
Date Wed, 29 Aug 2012 06:46:56 GMT
@Edward: I think you should consider a queue for exporting the new rows.
Just store the rowkey in a queue (you might want to consider looking at
http://cassandra-user-incubator-apache-org.3065146.n2.nabble.com/Distributed-work-queues-td5226248.html
)
and process that row every couple of minutes. Then manually delete columns
from that queue-row.

With kind regards,

Robin Verlangen
*Software engineer*
*
*
W http://www.robinverlangen.nl
E robin@us2.nl

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2012/8/29 Robin Verlangen <robin@us2.nl>

> "What this means is that eventually you will have 1 row in the secondary
> index table with 350K columns"
>
> Is this really true? I would have expected that Cassandra used internal
> index sharding/bucketing?
>
> With kind regards,
>
> Robin Verlangen
> *Software engineer*
> *
> *
> W http://www.robinverlangen.nl
> E robin@us2.nl
>
> Disclaimer: The information contained in this message and attachments is
> intended solely for the attention and use of the named addressee and may be
> confidential. If you are not the intended recipient, you are reminded that
> the information remains the property of the sender. You must not use,
> disclose, distribute, copy, print or rely on this e-mail. If you have
> received this message in error, please contact the sender immediately and
> irrevocably delete this message and any copies.
>
>
>
> 2012/8/29 Dave Brosius <dbrosius@mebigfatguy.com>
>
>> If i understand you correctly, you are only ever querying for the rows
>> where is_exported = false, and turning them into trues. What this means is
>> that eventually you will have 1 row in the secondary index table with 350K
>> columns that you will never look at.
>>
>> It seems to me you that perhaps you should just hold your own "manual
>> index" cf that points to non exported rows, and just delete those columns
>> when they are exported.
>>
>>
>>
>> On 08/28/2012 05:23 PM, Edward Kibardin wrote:
>>
>>> I have a column family with the secondary index. The secondary index is
>>> basically a binary field, but I'm using a string for it. The field called
>>> *is_exported* and can be *'true'* or *'false'*. After request all loaded
>>> rows are updated with *is_exported = 'false'*.
>>>
>>> I'm polling this column table each ten minutes and exporting new rows as
>>> they appear.
>>>
>>> But here the problem: I'm seeing that time for this query grows pretty
>>> linear with amount of data in column table, and currently it takes *from 12
>>> to 20 seconds (!!!) to find 5000 rows*. From my understanding, indexed
>>> request should not depend on number of rows in CF but from number of rows
>>> per one index value (cardinality), as it's just another hidden CF like:
>>>
>>>         "true" : rowKey1 rowKey2 rowKey3 ...
>>>         "false": rowKey1 rowKey2 rowKey3 ...
>>>
>>> I'm using Pycassa to query the data, here the code I'm using:
>>>
>>>         column_family = pycassa.ColumnFamily(**cassandra_pool,
>>> column_family_name, read_consistency_level=2)
>>>         is_exported_expr = create_index_expression('is_**exported',
>>> 'false')
>>>         clause = create_index_clause([is_**exported_expr], count = 5000)
>>>         column_family.get_indexed_**slices(clause)
>>>
>>> Am I doing something wrong, but I expect this operation to work MUCH
>>> faster.
>>>
>>> Any ideas or suggestions?
>>>
>>> Some config info:
>>>  - Cassandra 1.1.0
>>>  - RandomPartitioner
>>>  - I have 2 nodes and replication_factor = 2 (each server has a full
>>> data copy)
>>>  - Using AWS EC2, large instances
>>>  - Software raid0 on ephemeral drives
>>>
>>> Thanks in advance!
>>>
>>>
>>
>

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