[
https://issues.apache.org/jira/browse/CASSANDRA-1379?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13073398#comment-13073398
]
David King commented on CASSANDRA-1379:
---------------------------------------
bq. pulling the cache check out to a separate stage won't actually help clients
progress any more when you are i/o bound, since once they issue a
request-not-in-cache they have to wait for the physical read stage anyway.
For reddit's use-case there are requests that are high priority and almost
always memory bound (comments trees for active pages) and requests that are
lower priority and almost always disk-bound (voting buttons on external sites,
comments trees for old pages). It's very important that the high-priority tasks
not get blocked by lower priority tasks, and that means not allowing the lower
priority disk-bound tasks to clog up the read stage. It's okay if buttons on
external sites slow down. It's not okay if all of the comments pages for
extremely active pages slow down.
> Uncached row reads may block cached reads
> -----------------------------------------
>
> Key: CASSANDRA-1379
> URL: https://issues.apache.org/jira/browse/CASSANDRA-1379
> Project: Cassandra
> Issue Type: New Feature
> Components: Core
> Reporter: David King
> Assignee: Javier Canillas
> Priority: Minor
> Attachments: CASSANDRA-1379.patch
>
>
> The cap on the number of concurrent reads appears to cap the *total* number
> of concurrent reads instead of just capping the reads that are bound for
> disk. That is, given N concurrent readers if all of them are busy waiting on
> disk, even reads that can be served from the row cache will block waiting for
> them.
--
This message is automatically generated by JIRA.
For more information on JIRA, see: http://www.atlassian.com/software/jira
