Re: Cassandra GC tuning

Tue, 20 Sep 2022 06:04:35 -0700

Beyond this there are two decent tuning sets, but relatively dated at this point

Cassandra-8150 proposed a number of changes to defaults based on how it had been tuned at a specific large (competent) user:

Any Tobey wrote this guide around the 2.0/2.1 era, so it assumes things like jdk8 / CMS, but still has more rigor than most other guides you’ll find elsewhere and may help identify what’s going on even if the specific tuning isn’t super relevant in all cases:



On Sep 20, 2022, at 5:27 AM, Michail Kotsiouros via user <user@cassandra.apache.org> wrote:



Hello community,

BTW I am using Cassandra 3.11.4. From your comments, I understand that a CPU spike and maybe a long GC may be expected at the snapshot creation under specific circumstances. I will monitor the resources during snapshot creation. I will come back with more news.

 

Thanks a lot for your valuable input.

 

BR

MK

From: Jeff Jirsa <jji...@gmail.com>
Sent: Monday, September 19, 2022 20:06
To: user@cassandra.apache.org; Michail Kotsiouros <michail.kotsiou...@ericsson.com>
Subject: Re: Cassandra GC tuning

 

https://issues.apache.org/jira/browse/CASSANDRA-13019 is in 4.0, you may find that tuning those thresholds 

 

On Mon, Sep 19, 2022 at 9:50 AM Jeff Jirsa <jji...@gmail.com> wrote:

Snapshots are probably actually caused by a spike in disk IO and disk latency, not GC (you'll see longer STW pauses as you get to a safepoint if that disk is hanging). This is especially problematic on SATA SSDs, or nVME SSDs with poor IO scheduler tuning.  There's a patch somewhere to throttle hardlinks to try to mitigate this. 

 

On Mon, Sep 19, 2022 at 3:45 AM Michail Kotsiouros via user <user@cassandra.apache.org> wrote:

Hello community,

I observe some GC pauses while trying to create snapshots of a keyspace. The GC pauses as such are not long, even though they are reported in logs. The problem is the CPU utilization which affects other applications deployed in my server.

Do you have any articles or recommendations about tuning GC in Cassandra?

 

Thank you in advance.

BR

MK

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