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From Benedict Elliott Smith <belliottsm...@datastax.com>
Subject Re: impact of update operation to read operation
Date Mon, 10 Feb 2014 21:25:19 GMT
Also, a major compaction doesn't flush the memtable. If the memtable is
still full, reads may take slightly longer as they may have to be merged
with any on-disk data before being served.


On 10 February 2014 21:18, Tupshin Harper <tupshin@tupshin.com> wrote:

> You don't mention disks and RAM,  but I would assume that the additional
> data meant that you could now cache a lower percentage and that you have to
> seek on disk more often.
>
> -Tupshin
> On Feb 10, 2014 4:14 PM, "Jiaan Zeng" <l.allen09@gmail.com> wrote:
>
>> Hi All,
>>
>> I am using Cassandra 1.2.4. I wonder if update operation has
>> *permanent* impacts on read operation. Below is the scenario.
>>
>> Previously, a read only workload runs against one column family and
>> has 4000 qps. Later, a read-update mixed workload  runs against the
>> same column family. After that, the read only workload runs again but
>> it could not get 4000 qps, only get 3500 qps. After a manual major
>> compaction is issued through command line, the read only workload gets
>> 3600 qps which seems to tell major compaction does not help much.
>>
>> Did anyone have similar experiences? Any idea why this is happening?
>> Thanks.
>>
>> --
>> Regards,
>> Jiaan
>>
>

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