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From Jon Haddad <...@jonhaddad.com>
Subject Re: Disk space utilization by from some Cassandra
Date Wed, 21 Aug 2019 16:01:10 GMT
This advice hasn't been valid for a long time now for most use cases.  The
only time you need to reserve 50% disk space is if you're going to be
running major compactions against a table in your cluster that occupies 50%
of its total disk space.  Nowadays, that's far less common than it was when
your only option was STCS and majors to clean out your tombstones and
tombstoned data.

Even if you need to run majors regularly, if the tables you're running them
on are using 10% of your disk space you only need a little over 10% free to
run it.

If you're using TWCS and TTLs, you can run 80-90% disk usage and be fine in
a lot of cases.

The blanket advice of 50% free needs to die in a fire, it's flat out wrong
*as a rule* and expensive.  There are cases in which it is valid, but there
are far fewer valid applications of it than not.

Jon



On Wed, Aug 21, 2019 at 6:53 AM Stefan Miklosovic <
stefan.miklosovic@instaclustr.com> wrote:

> Hi,
>
> for example compaction uses a lot of disk space. It is quite common so
> it is not safe to have your disk utilised like on 85% because
> compactions would not have room to comapact and that node would be
> stuck. This happens in production quite often.
>
> Hence, having it on 50% and having big buffer to do compaction is good
> idea. If it is all compacted, it should go back to normal under 50%
> (or what figure you have).
>
> On Wed, 21 Aug 2019 at 14:33, <yanga.zukelwa@condorgreen.com> wrote:
> >
> > Good day,
> >
> >
> >
> > I’m running the monitoring script for disk space utilization set the
> benchmark to 50%. Currently am getting the alerts from some of the nodes
> >
> > About disk space greater than 50%.
> >
> >
> >
> > Is there a way, I can quickly figure out why the space has increased and
> how I can maintain the disk space used by Cassandra to be below the
> benchmark at all the times.
> >
> >
> >
> > Any ideas would be much appreciated.
> >
> >
> >
> > Sent from Mail for Windows 10
> >
> >
>
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