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From Brian Tarbox <tar...@cabotresearch.com>
Subject Re: help turning compaction..hours of run to get 0% compaction....
Date Mon, 07 Jan 2013 21:58:34 GMT
The problem I see is that it already takes me more than 24 hours just to
load my data...during which time the logs say I'm spending tons of time
doing compaction.  For example in the last 72 hours I'm consumed* 20
hours*per machine on compaction.

Can I conclude from that than I should be (perhaps drastically) increasing
my compaction_mb_per_sec on the theory that I'm getting behind?

The fact that it takes me 3 days or more to run a test means its hard to
just play with values and see what works best, so I'm trying to understand
the behavior in detail.

Thanks.

Brain


On Mon, Jan 7, 2013 at 4:13 PM, Michael Kjellman <mkjellman@barracuda.com>wrote:

> http://www.datastax.com/dev/blog/when-to-use-leveled-compaction
>
> "If you perform at least twice as many reads as you do writes, leveled
> compaction may actually save you disk I/O, despite consuming more I/O for
> compaction. This is especially true if your reads are fairly random and
> don’t focus on a single, hot dataset."
>
> From: Brian Tarbox <tarbox@cabotresearch.com>
> Reply-To: "user@cassandra.apache.org" <user@cassandra.apache.org>
> Date: Monday, January 7, 2013 12:56 PM
> To: "user@cassandra.apache.org" <user@cassandra.apache.org>
> Subject: Re: help turning compaction..hours of run to get 0%
> compaction....
>
> I have not specified leveled compaction so I guess I'm defaulting to size
> tiered?  My data (in the column family causing the trouble) insert once,
> ready many, update-never.
>
> Brian
>
>
> On Mon, Jan 7, 2013 at 3:13 PM, Michael Kjellman <mkjellman@barracuda.com>wrote:
>
>> Size tiered or leveled compaction?
>>
>> From: Brian Tarbox <tarbox@cabotresearch.com>
>> Reply-To: "user@cassandra.apache.org" <user@cassandra.apache.org>
>> Date: Monday, January 7, 2013 12:03 PM
>> To: "user@cassandra.apache.org" <user@cassandra.apache.org>
>> Subject: help turning compaction..hours of run to get 0% compaction....
>>
>> I have a column family where I'm doing 500 inserts/sec for 12 hours or so
>> at time.  At some point my performance falls off a cliff due to time spent
>> doing compactions.
>>
>> I'm seeing row after row of logs saying that after 1 or 2 hours of
>> compactiing it reduced to 100% of 99% of the original.
>>
>> I'm trying to understand what direction this data points me to in term of
>> configuration change.
>>
>>    a) increase my compaction_throughput_mb_per_sec because I'm falling
>> behind (am I falling behind?)
>>
>>    b) enable multi-threaded compaction?
>>
>> Any help is appreciated.
>>
>> Brian
>>
>> ----------------------------------
>> Join Barracuda Networks in the fight against hunger.
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>>
>
>
> ----------------------------------
> Join Barracuda Networks in the fight against hunger.
> To learn how you can help in your community, please visit:
> http://on.fb.me/UAdL4f
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>

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