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From "Jonathan Ellis (JIRA)" <>
Subject [jira] Commented: (CASSANDRA-1972) Default concurrency values are improperly proportioned
Date Wed, 12 Jan 2011 18:24:45 GMT


Jonathan Ellis commented on CASSANDRA-1972:

Yes, this sounds like a pretty straightforward win.  Have you done testing on better values,

> Default concurrency values are improperly proportioned
> ------------------------------------------------------
>                 Key: CASSANDRA-1972
>                 URL:
>             Project: Cassandra
>          Issue Type: Bug
>            Reporter: Stu Hood
>            Assignee: Stu Hood
>            Priority: Minor
>             Fix For: 0.7.1
> The "default"/"suggested" {{concurrent_reads}} value is much too low. It assumes that
CPU will be the bottleneck, rather than IO, and for most deployments, this will not be the
case. Additionally it is better to be queued for IO in the kernel or on your device than in
user space, because the former work to optimize queue order.
> Additionally, reads are much cheaper than writes in terms of CPU time (since writes can
experience contention due to retries), so while {{concurrent_writes}} should probably factor
in the number of cores on the machine, {{concurrent_reads}} should probably be calculated
purely by number of spindles.

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