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From "Jonathan Ellis (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-9318) Bound the number of in-flight requests at the coordinator
Date Sun, 28 Jun 2015 16:38:05 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-9318?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14604767#comment-14604767
] 

Jonathan Ellis commented on CASSANDRA-9318:
-------------------------------------------

I think you're [Aleksey] confusing replica-side and coordinator-side.  There are no separate
write and read queues on the coordinator and there probably shouldn't be.

Again, let's avoid the temptation to boil the ocean.  We can make a simple improvement by
bounding the total outstanding request size that we have in flight on the coordinator side.
 Once we exceed that global limit we stop reading additional requests.  That's it.

There are lots of ways we can tweak this (e.g. estimating how many rows a read is likely to
return) but making that change alone will be a big improvement and is something that we can
reasonably do for 2.1.x, so let's not hold it up for grand rewrites of all the things.

> Bound the number of in-flight requests at the coordinator
> ---------------------------------------------------------
>
>                 Key: CASSANDRA-9318
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-9318
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Ariel Weisberg
>            Assignee: Ariel Weisberg
>             Fix For: 2.1.x, 2.2.x
>
>
> It's possible to somewhat bound the amount of load accepted into the cluster by bounding
the number of in-flight requests and request bytes.
> An implementation might do something like track the number of outstanding bytes and requests
and if it reaches a high watermark disable read on client connections until it goes back below
some low watermark.
> Need to make sure that disabling read on the client connection won't introduce other
issues.



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