cassandra-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Victor Chen <victor.h.c...@gmail.com>
Subject Re: Restarting nodes and reported load
Date Thu, 01 Jun 2017 21:32:37 GMT
Regarding mtime, I'm just talking about using something like the following
(assuming you are on linux) "find *pathtoyourdatadir *-mtime -1 -ls" which
will find all files in your datadir last modifed within the past 24h. You
can compare increase in your reported nodetool load within the past N days
and then use the same period of time to look for files modified that could
match that size. Not really sure what sort of load or how long that would
take on 3-4T of data though.

Regarding compactionstats and tpstats, I would just be interested if there
are increasing "pending" tasks for either. Did you say you observed latency
issues or degraded performance or not?

What version of java/cassandra did you say you were running and what type
of gc are you using?

Regarding not showing a node not creating "DOWN" entry in log, if a node
experiences a sufficiently long gc pause (I'm not sure what the threshold
is, maybe somebody more knowledgeable can chime in?), then even though the
node itself still "thinks" it's up, *other* nodes will mark it as DN, thus
you wouldn't see a "is now DOWN" entry in the system.log of the gc-ing
node, but you *would* see a "is now DOWN" entry in the system.log of the
remote nodes (and a corresponding "is now UP" entry when the node comes out
of its gc pause. Assuming the logs have not been rotated off, if you just
grep system.log for "DOWN" on your nodes, that usually reveals a useful
timestamp from where to start looking on the problematic node's system.log
or gc.log.

Do you have peristent cpu/memory disk io/ space monitoring mechanisms? You
should think about putting something in place to gathering that info if you
don't ... I find myself coming back to Al Tobey's tuning guide
<https://tobert.github.io/pages/als-cassandra-21-tuning-guide.html>
frequently if nothing else for the tools he mentions and notes on the java
gc. I want to say heap size of 15G sounds a little high but I am starting
to talk a bit out of my depth when it comes to java tuning. see
datastax's official
cassandra 2.1 jvm tuning doc
<http://docs.datastax.com/en/cassandra/2.1/cassandra/operations/ops_tune_jvm_c.html>
and also this stackoverflow thread.
<https://stackoverflow.com/questions/30207779/optimal-jvm-settings-for-cassandra>

good luck!



On Thu, Jun 1, 2017 at 4:06 PM, Daniel Steuernol <daniel@sendwithus.com>
wrote:

> I'll try to capture answer to questions in the last 2 messages.
>
> Network traffic looks pretty steady overall. About 0.5 up to 2
> megabytes/s. The cluster handles about 100k to 500k operations per minute,
> right now the read/write comparison is about 50/50 right now, eventually
> though it will probably be 70% writes and 30% reads.
>
> There does seem to be some nodes that are affected more frequently then
> others. I haven't captured cpu/memory stats vs other nodes at the time the
> problem is occurring, I will do that next time it happens. Also I will look
> at compaction stats and tpstats, what are some things that I should be
> looking for in tpstats in particular, I'm not exactly sure how to read the
> output from that command.
>
> The heap size is set to 15GB on each node, and each node has 60GB of ram
> available.
>
> In regards to the "... is now DOWN" messages. I'm unable to find one in
> the system.log for a time I know that a node was having problems. I've
> built a system that polls nodetool status and parses the output, and if it
> sees a node reporting as DN it sends a message to a slack channel. Is it
> possible for a node to report as DN, but not have the message show up in th
> log?
> The system polling nodetool status is not the status that was reported as
> DN.
>
> I'm a bit unclear about the last point about mtime/size of files and how
> to check, can you provide more information there?
>
> Thanks for the all the help, I really appreciate it.
>
>
>
> On Jun 1 2017, at 10:33 am, Victor Chen <victor.h.chen@gmail.com> wrote:
>
>> Hi Daniel,
>>
>> In my experience when a node shows DN and then comes back up by itself
>> that sounds some sort of gc pause (especially if nodtool status when run
>> from the "DN" node itself shows it is up-- assuming there isn't a spotty
>> network issue). Perhaps I missed this info due to length of thread but have
>> you shared info about the following?
>>
>>    - cpu/memory usage of affected nodes (are all nodes affected
>>    comparably, or some more than others?)
>>    - nodetool compactionstats and tpstats output (especially as the )
>>    - what is your heap size set to?
>>    - system.log and gc.logs: for investigating node "DN" symptoms I will
>>    usually start by noting the timestamp of the "123.56.78.901 is now DOWN"
>>    entries in system.log of other nodes to tell me where to look in system.log
>>    of node in question. Then it's a question answer "what was this node doing
>>    up to that point?"
>>    - mtime/size of files in data directory-- which files are growing in
>>    size?
>>
>> That will help reduce how much we need to speculate. I don't think you
>> should need to restart cassandra every X days if things are optimally
>> configured for your read/write pattern-- at least I would not want to use
>> something where that is the normal expected behavior (and I don't believe
>> cassandra is one of those sorts of things).
>>
>> On Thu, Jun 1, 2017 at 11:40 AM, daemeon reiydelle <daemeonr@gmail.com>
>> wrote:
>>
>> Some random thoughts; I would like to thank you for giving us an
>> interesting problem. Cassandra can get boring sometimes, it is too stable.
>>
>> - Do you have a way to monitor the network traffic to see if it is
>> increasing between restarts or does it seem relatively flat?
>> - What activities are happening when you observe the (increasing)
>> latencies? Something must be writing to keyspaces, something I presume is
>> reading. What is the workload?
>> - when using SSD, there are some /devices optimizations for SSD's. I
>> wonder if those were done (they will cause some IO latency, but not like
>> this)
>>
>>
>>
>>
>>
>>
>>
>> *Daemeon C.M. ReiydelleUSA (+1) 415.501.0198London (+44) (0) 20 8144 9872*
>>
>>
>>
>> On Thu, Jun 1, 2017 at 7:18 AM, Daniel Steuernol <daniel@sendwithus.com>
>> wrote:
>>
>> I am just restarting cassandra. I'm not having any disk space issues I
>> think, but we're having issues where operations have increased latency, and
>> these are fixed by a restart. It seemed like the load reported by nodetool
>> status might be helpful in understanding what is going wrong but I'm not
>> sure. Another symptom is that nodes will report as DN in nodetool status
>> and then come back up again just a minute later.
>>
>> I'm not really sure what to track to find out what exactly is going wrong
>> on the cluster, so any insight or debugging techniques would be super
>> helpful
>>
>>
>> On May 31 2017, at 5:07 pm, Anthony Grasso <anthony.grasso@gmail.com>
>> wrote:
>>
>> Hi Daniel,
>>
>> When you say that the nodes have to be restarted, are you just restarting
>> the Cassandra service or are you restarting the machine?
>> How are you reclaiming disk space at the moment? Does disk space free up
>> after the restart?
>>
>> Regarding storage on nodes, keep in mind the more data stored on a node,
>> the longer some operations to maintain that data will take to complete. In
>> addition, the more data that is on each node, the long it will take to
>> stream data to other nodes. Whether it is replacing a down node or
>> inserting a new node, having a large amount of data on each node will mean
>> that it takes longer for a node to join the cluster if it is streaming the
>> data.
>>
>> Kind regards,
>> Anthony
>>
>> On 30 May 2017 at 02:43, Daniel Steuernol <daniel@sendwithus.com> wrote:
>>
>> The cluster is running with RF=3, right now each node is storing about
>> 3-4 TB of data. I'm using r4.2xlarge EC2 instances, these have 8 vCPU's, 61
>> GB of RAM, and the disks attached for the data drive are gp2 ssd ebs
>> volumes with 10k iops. I guess this brings up the question of what's a good
>> marker to decide on whether to increase disk space vs provisioning a new
>> node?
>>
>>
>>
>> On May 29 2017, at 9:35 am, tommaso barbugli <tbarbugli@gmail.com>
>> wrote:
>>
>> Hi Daniel,
>>
>> This is not normal. Possibly a capacity problem. Whats the RF, how much
>> data do you store per node and what kind of servers do you use (core count,
>> RAM, disk, ...)?
>>
>> Cheers,
>> Tommaso
>>
>> On Mon, May 29, 2017 at 6:22 PM, Daniel Steuernol <daniel@sendwithus.com>
>> wrote:
>>
>>
>> I am running a 6 node cluster, and I have noticed that the reported load
>> on each node rises throughout the week and grows way past the actual disk
>> space used and available on each node. Also eventually latency for
>> operations suffers and the nodes have to be restarted. A couple questions
>> on this, is this normal? Also does cassandra need to be restarted every few
>> days for best performance? Any insight on this behaviour would be helpful.
>>
>> Cheers,
>> Daniel
>> --------------------------------------------------------------------- To
>> unsubscribe, e-mail: user-unsubscribe@cassandra.apache.org For
>> additional commands, e-mail: user-help@cassandra.apache.org
>>
>>
>> --------------------------------------------------------------------- To
>> unsubscribe, e-mail: user-unsubscribe@cassandra.apache.org For
>> additional commands, e-mail: user-help@cassandra.apache.org
>>
>>
>> --------------------------------------------------------------------- To
>> unsubscribe, e-mail: user-unsubscribe@cassandra.apache.org For
>> additional commands, e-mail: user-help@cassandra.apache.org
>>
>>
>>
>>

Mime
View raw message