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From Jonathan Ellis <jbel...@gmail.com>
Subject Re: get_slice slow
Date Wed, 25 Aug 2010 13:23:15 GMT
Cassandra doesn't deserialize entire rows to read a single column.

On Tue, Aug 24, 2010 at 11:25 PM, Artie Copeland <yeslinux.now@gmail.com> wrote:
> Have you tried using a super column, it seems that having a row with over
> 100K columns and growing would be alot for cassandra to deserialize?  what
> is iostat and jmeter telling you? it would be interesting to see that data.
>  also what are you using for you key or row caching?  do you need to use a
> quorum consistency as that can slow down reads as well, can you use a lower
> consistency level?
>
> Artie
> On Tue, Aug 24, 2010 at 9:14 PM, B. Todd Burruss <bburruss@real.com> wrote:
>>
>> i am using get_slice to pull columns from a row to emulate a queue.
>>  column names are TimeUUID and the values are small, < 32 bytes.  simple
>> ColumnFamily.
>>
>> i am using SlicePredicate like this to pull the first ("oldest") column in
>> the row:
>>
>>        SlicePredicate predicate = new SlicePredicate();
>>        predicate.setSlice_range(new SliceRange(new byte[] {}, new byte[]
>> {}, false, 1));
>>
>>        get_slice(rowKey, colParent, predicate, QUORUM);
>>
>> once i get the column i remove it.  so there are a lot of gets and
>> mutates, leaving lots of deleted columns.
>>
>> get_slice starts off performing just fine, but then falls off dramatically
>> as the number of columns grows.  at its peak there are 100,000 columns and
>> get_slice is taking over 100ms to return.
>>
>> i am running a single instance of cassandra 0.7 on localhost, default
>> config.  i've done some googling and can't find any tweaks or tuning
>> suggestions specific to get_slice.  i already know about separating
>> commitlog and data, watching iostat, GC, etc.
>>
>> any low hanging tuning fruit anyone can think of?  in 0.6 i recall an
>> index for columns, maybe that is what i need?
>>
>> thx
>
>
>
> --
> http://yeslinux.org
> http://yestech.org
>



-- 
Jonathan Ellis
Project Chair, Apache Cassandra
co-founder of Riptano, the source for professional Cassandra support
http://riptano.com

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