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From "Jeff Jirsa"<jji...@apache.org>
Subject Re: Information on Cassandra
Date Fri, 02 Jun 2017 18:01:51 GMT


On 2017-06-01 09:09 (-0700), "Harper, Paul" <paul.harper@Aspect.com> wrote: 
> Hello All,
> 
> I'm about 3 months into support several clusters of Cassandra databases. I recently subscribed
to this email list and I receive lots of interesting emails most of which I don't understand.
I feel like I have a pretty good grasp on Cassandra, I would like to know what types of this
should I be checking on a daily, weekly or monthly basis. Many of the email I see in this
string are on subjects I've never had to look at so far. So I'm wondering what is it that
I should be monitoring or doing or I should know. I would appreciate it any advice or guidance
you can provide. Please to my email and not the group listing  unless it's something that
maybe helpful to others.
> 

The good news is that cassandra can run for years without any intervention, especially if
you're not pushing the limits.

At a high level, you should be watching:
- Read/writes per second. Your application may warn you if these change, but catching it before
it impacts your application is always nice. 
- Latencies (how long does each read/write take, and is that getting worse over time, which
may indicate a problem brewing)
- How much data is on each node (hopefully it's pretty even)
- How many sstables are on each node (hopefully it's pretty even)
- GC pause times (you're probably using parnew/cms, most metrics packages will know how to
graph those as two distinct lines - seeing long pauses is a good hint that things are starting
to get bad)
- How often are you running repair? Is repair succeeding? Is it failing? If you delete data,
you need to repair (successfully, all nodes) at least once every gc_grace_seconds (by default
10 days). 
- Whether or not schema versions match - if schema diverges, you could have a big problem
brewing.






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