[jira] [Commented] (CASSANDRA-7402) limit the on heap memory available to requests

["Rick Branson (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-7402?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14055168#comment-14055168 ] 

Rick Branson commented on CASSANDRA-7402:
-----------------------------------------

The more "practical" thing here is to make sure nothing on the read/write paths can potentially allocate big chunks of heap. If one looks at the read/write paths for something like PostgreSQL, they have made sure that the only potentially large allocations (sorts, hash-joins, etc) occur in a very controlled manner and have hard limits attached to them that can be configured. This seems like a reasonable thing to ask for at this stage in Cassandra's life.

> limit the on heap memory available to requests
> ----------------------------------------------
>
>                 Key: CASSANDRA-7402
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-7402
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: T Jake Luciani
>             Fix For: 3.0
>
>
> When running a production cluster one common operational issue is quantifying GC pauses caused by ongoing requests.
> Since different queries return varying amount of data you can easily get your self into a situation where you Stop the world from a couple of bad actors in the system.  Or more likely the aggregate garbage generated on a single node across all in flight requests causes a GC.
> We should be able to set a limit on the max heap we can allocate to all outstanding requests and track the garbage per requests to stop this from happening.  It should increase a single nodes availability substantially.
> In the yaml this would be
> {code}
> total_request_memory_space_mb: 400
> {code}
> It would also be nice to have either a log of queries which generate the most garbage so operators can track this.  Also a histogram.



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