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From Nate McCall <>
Subject Re: Back to the futex()? :(
Date Tue, 09 Feb 2016 19:25:17 GMT
I noticed you have authentication enabled. Make sure you set the following:

- the replication factor for the system_auth keyspace should equal the
number of nodes
- permissions_validity_in_ms is a permission cache timeout. If you are not
doing dynamic permissions or creating/revoking frequently, turn this WAY up

May not be the immediate reason, but the above are definitely not helping
if set at defaults.

On Sat, Feb 6, 2016 at 6:49 PM, Will Hayworth <>

> Additionally: this isn't the futex_wait bug (or at least it shouldn't
> be?). Amazon says
> <> that was
> fixed several kernel versions before mine, which
> is 4.1.10-17.31.amzn1.x86_64. And the reason my heap is so large is
> because, per CASSANDRA-9472, we can't use offheap until 3.4 is released.
> Will
> ___________________________________________________________
> Will Hayworth
> Developer, Engagement Engine
> Atlassian
> My pronoun is "they". <>
> On Sat, Feb 6, 2016 at 3:28 PM, Will Hayworth <>
> wrote:
>> *tl;dr: other than CAS operations, what are the potential sources of lock
>> contention in C*?*
>> Hi all! :) I'm a novice Cassandra and Linux admin who's been preparing a
>> small cluster for production, and I've been seeing something weird. For
>> background: I'm running 3.2.1 on a cluster of 12 EC2 m4.2xlarges (32 GB
>> RAM, 8 HT cores) backed by 3.5 TB GP2 EBS volumes. Until late yesterday,
>> that was a cluster of 12 m4.xlarges with 3 TB volumes. I bumped it because
>> while backloading historical data I had been seeing awful throughput (20K
>> op/s at CL.ONE). I'd read through Al Tobey's *amazing* C* tuning guide
>> <> once
>> or twice before but this time I was careful and fixed a bunch of defaults
>> that just weren't right, in cassandra.yaml/JVM options/block device
>> parameters. Folks on IRC were super helpful as always (hat tip to Jeff
>> Jirsa in particular) and pointed out, for example, that I shouldn't be
>> using DTCS for loading historical data--heh. After changing to LTCS,
>> unbatching my writes* and reserving a CPU core for interrupts and fixing
>> the clocksource to TSC, I finally hit 80K early this morning. Hooray! :)
>> Now, my question: I'm still seeing a *ton* of blocked processes in the
>> vmstats, anything from 2 to 9 per 10 second sample period--and this is
>> before EBS is even being hit! I've been trying in vain to figure out what
>> this could be--GC seems very quiet, after all. On Al's page's advice, I've
>> been running strace and, indeed, I've been seeing *tens of thousands of
>> futex() calls* in periods of 10 or 20 seconds. What eludes me is *where* this
>> lock contention is coming from. I'm not using LWTs or performing CAS
>> operations of which I'm aware. Assuming this isn't a red herring, what
>> gives?
>> Sorry for the essay--I just wanted to err on the side of more
>> context--and *thank you* for any advice you'd like to offer,
>> Will
>> P.S. More background if you'd like--I'm running on Amazon Linux 2015.09,
>> using jemalloc 3.6, JDK 1.8.0_65-b17. Here <> is
>> my cassandra.yaml and here <> are my JVM
>> args. I realized I neglected to adjust memtable_flush_writers as I was
>> writing this--so I'll get on that. Aside from that, I'm not sure what to
>> do. (Thanks, again, for reading.)
>> * They were batched for consistency--I'm hoping to return to using them
>> when I'm back at normal load, which is tiny compared to backloading, but
>> the impact on performance was eye-opening.
>> ___________________________________________________________
>> Will Hayworth
>> Developer, Engagement Engine
>> Atlassian
>> My pronoun is "they". <>

Nate McCall
Austin, TX

Co-Founder & Sr. Technical Consultant
Apache Cassandra Consulting

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