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From Artur Kronenberg <artur.kronenb...@openmarket.com>
Subject Re: How to extract information from commit log?
Date Wed, 19 Mar 2014 08:53:42 GMT
Hi,

we did something similar. We did utilize some cassandra code though and 
wrote a custom commitlog reader that outputs our data into a readable form.

You can look here: 
http://grepcode.com/file/repo1.maven.org/maven2/org.apache.cassandra/cassandra-all/1.1.9/org/apache/cassandra/db/commitlog/CommitLogReplayer.java

This code is used to replay commitlogs when starting up cassandra. It 
has the ability to deserialize and transform the data into what you'll need.

-- artur


On 18/03/14 19:32, Han,Meng wrote:
>
> Hi Jonathan,
>
> Thank you for the timely reply. I am doing this experiment on a 
> continuous basis. To be more specific, I will issue a large amount of 
> read and write operations to a particular key in a short time 
> interval. I'd like to know the order that write operations happens at 
> each replica. TImestamps definitely help to determine order, but the 
> WRITETIME and SStable2Json both looks me only return the timestamps 
> when that key was updated the moment the WRITETIME/SStable2Json is 
> issued. It looks like a one time thing to me. Or put in another way, 
> if I want to get the write time for all write operations in that short 
> invertal to determine a total order for write on that replia I have to 
> constantly issue WRITETIME to this replica?  Correct me if I am wrong 
> here.
>
> Light me up pleeeeeeeeeease!
>
> On Tue, 18 Mar 2014 15:05:07 -0400, Jonathan Lacefield wrote:
>
>> Hello,
>>   Is this a one time investigative item or are you looking to set 
>> something up to do this continuously?  Don't recommend trying to read 
>> the commit log.
>>   You can always use the WRITETIME function in CQL or look within 
>> SSTables via the SStable2Json utility to see write times for 
>> particular versions of partitions.
>> Jonathan
>>
>> Jonathan Lacefield
>> Solutions Architect, DataStax
>> (404) 822 3487
>> <http://www.linkedin.com/in/jlacefield>
>> <http://www.datastax.com/what-we-offer/products-services/training/virtual-training>
>>
>>
>> On Tue, Mar 18, 2014 at 2:25 PM, Han,Meng <menghan@ufl.edu 
>> <mailto:menghan@ufl.edu>> wrote:
>>
>>     Hi Cassandra hackers!
>>
>>     I have a question regarding extracting useful information from
>>     commit log.
>>
>>     Since its a binary log, how should I extract information such as
>>     timestamp, values from it? Does anyone know any binary log reader
>>     that I can use directly to read commit log?
>>     If there is no such reader, could someone give me some advice hwo
>>     I can wrote such a reader?
>>
>>     Particularly, I want to know the order that write operations
>>     happens at each replica(cassandra server node) along with their
>>     timestamps, Does anyone know other methods how I can get this
>>     information without instrumenting Cassandra code?
>>
>>     Any help is appreciated!
>>
>>     Cheers,
>>     Meng
>>


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