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Date: Tue, 23 Dec 2014 22:21:13 +0000 (UTC)
From: "Cheng Ren (JIRA)" <jira@apache.org>
To: commits@cassandra.apache.org
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Subject: [jira] [Commented] (CASSANDRA-8518) Cassandra Query Request Size
 Estimator
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    [ https://issues.apache.org/jira/browse/CASSANDRA-8518?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14257606#comment-14257606 ] 

Cheng Ren commented on CASSANDRA-8518:
--------------------------------------

Thanks for your reply.
The feature you suggested is very useful, and we will definitely  consider it in future upgrade. But as you mentioned in CASSANDRA-7402, it's not going to solve the underlying OOM issue caused by large response data of requests. 
The feature we are eager to have should help to prevent OOM in system itself. What we are proposing here is to take advantage of existing code and build a better memory estimator so that system can throttle requests. Please let us know If there is any other related issue. We also would like to hear your feedback on our proposal. 

Thanks

> Cassandra Query Request Size Estimator
> --------------------------------------
>
>                 Key: CASSANDRA-8518
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-8518
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Cheng Ren
>
> We have been suffering from cassandra node crash due to out of memory for a long time. The heap dump from the recent crash shows there are 22 native transport request threads each of which consumes 3.3% of heap size, taking more than 70% in total.  
> Heap dump:
> !https://dl-web.dropbox.com/get/attach1.png?_subject_uid=303980955&w=AAAVOoncBoZ5aOPbDg2TpRkUss7B-2wlrnhUAv19b27OUA|height=400,width=600!
> Expanded view of one thread:
> !https://dl-web.dropbox.com/get/Screen%20Shot%202014-12-18%20at%204.06.29%20PM.png?_subject_uid=303980955&w=AACUO4wrbxheRUxv8fwQ9P52T6gBOm5_g9zeIe8odu3V3w|height=400,width=600!
> The cassandra we are using now (2.0.4) utilized MemoryAwareThreadPoolExecutor as the request executor and provided a default request size estimator which constantly returns 1, meaning it limits only the number of requests being pushed to the pool. To have more fine-grained control on handling requests and better protect our node from OOM issue, we propose implementing a more precise estimator. 
> Here is our two cents:
> For update/delete/insert request: Size could be estimated by adding size of all class members together.
> For scan query, the major part of the request is response, which can be estimated from the history data. For example if we receive a scan query on a column family for a certain token range, we keep track of its response size used as the estimated response size for later scan query on the same cf. 
> For future requests on the same cf, response size could be calculated by token range*recorded size/ recorded token range. The request size should be estimated as (query size + estimated response size).
> We believe what we're proposing here can be useful for other people in the Cassandra community as well. Would you mind providing us feedbacks? Please let us know if you have any concerns or suggestions regarding this proposal.
> Thanks,
> Cheng


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