Re: Lot of GC on two nodes out of 7

[Anishek Agarwal]

@Jeff i was just trying to follow some more advice given above, I
personally still think a larger newGen heap size would be better.

@Johnathan I will post the whole logs, I have restarted the nodes with
additional changes most probably tomorrow or day after i will put out the
gc logs.

the problem still exists on two nodes. too much time spent in GC,
additionally I tried to print the state of cluster via my application to
see what is happening and i see that the node with high GC has a lot of
 "inflight Queries" -- almost 1100 and other nodes is all 0.

the cfhistograms for all nodes show the approx the same number of reads. --
so i am thinking the above phenomenon is happening since the node is
spending time in gc.

also looking at the Load Balancing policy on client its new
TokenAwarePolicy(new DCAwareRoundRobinPolicy())

if you have any other ideas please keep posting them.

thanks
anishek

On Sat, Mar 5, 2016 at 12:54 AM, Jonathan Haddad  wrote:

> Without looking at your GC logs (you never posted a gist), my assumption
> would be you're doing a lot of copying between survivor generations, and
> they're taking a long time.  You're probably also copying a lot of data to
> your old gen as a result of having full-ish survivor spaces to begin with.
>
> On Thu, Mar 3, 2016 at 10:26 PM Jeff Jirsa 
> wrote:
>
>> I’d personally would have gone the other way – if you’re seeing parnew,
>> increasing new gen instead of decreasing it should help drop (faster)
>> rather than promoting to sv/oldgen (slower) ?
>>
>>
>>
>> From: Anishek Agarwal
>> Reply-To: "user@cassandra.apache.org"
>> Date: Thursday, March 3, 2016 at 8:55 PM
>>
>> To: "user@cassandra.apache.org"
>> Subject: Re: Lot of GC on two nodes out of 7
>>
>> Hello,
>>
>> Bryan, most of the partition sizes are under 45 KB
>>
>> I have tried with concurrent_compactors : 8 for one of the nodes still no
>> improvement,
>> I have tried max_heap_Size : 8G, no improvement.
>>
>> I will try the newHeapsize of 2G though i am sure CMS will be a longer
>> then.
>>
>> Also doesn't look like i mentioned what type of GC was causing the
>> problems. On both the nodes its the ParNewGC thats taking long for each run
>> and too many runs are happening in succession.
>>
>> anishek
>>
>>
>> On Fri, Mar 4, 2016 at 5:36 AM, Bryan Cheng 
>> wrote:
>>
>>> Hi Anishek,
>>>
>>> In addition to the good advice others have given, do you notice any
>>> abnormally large partitions? What does cfhistograms report for 99%
>>> partition size? A few huge partitions will cause very disproportionate load
>>> on your cluster, including high GC.
>>>
>>> --Bryan
>>>
>>> On Wed, Mar 2, 2016 at 9:28 AM, Amit Singh F 
>>> wrote:
>>>
 Hi Anishek,



 We too faced similar problem in 2.0.14 and after doing some research we
 config few parameters in Cassandra.yaml and was able to overcome GC pauses
 . Those are :



 · memtable_flush_writers : increased from 1 to 3 as from
 tpstats output  we can see mutations dropped so it means writes are getting
 blocked, so increasing number will have those catered.

 · memtable_total_space_in_mb : Default (1/4 of heap size), can
 lowered because larger long lived objects will create pressure on HEAP, so
 its better to reduce some amount of size.

 · Concurrent_compactors : Alain righlty pointed out this i.e
 reduce it to 8. You need to try this.



 Also please check whether you have mutations drop in other nodes or not.



 Hope this helps in your cluster too.



 Regards

 Amit Singh

 *From:* Jonathan Haddad [mailto:j...@jonhaddad.com]
 *Sent:* Wednesday, March 02, 2016 9:33 PM
 *To:* user@cassandra.apache.org
 *Subject:* Re: Lot of GC on two nodes out of 7



 Can you post a gist of the output of jstat -gccause (60 seconds
 worth)?  I think it's cool you're willing to experiment with alternative
 JVM settings but I've never seen anyone use max tenuring threshold of 50
 either and I can't imagine it's helpful.  Keep in mind if your objects are
 actually reaching that threshold it means they've been copied 50x (really
 really slow) and also you're going to end up spilling your eden objects
 directly into your old gen if your survivor is full.  Considering the small
 amount of memory you're using for heap I'm really not surprised you're
 running into problems.



 I recommend G1GC + 12GB heap and just let it optimize itself for almost
 all cases with the latest JVM versions.



 On Wed, Mar 2, 2016 at 6:08 AM Alain RODRIGUEZ 
 wrote:

 It looks like you are doing a good work with this cluster and know a
 lot about JVM, that's good :-).



 our machine 

Re: Lot of GC on two nodes out of 7

[Jonathan Haddad]

Without looking at your GC logs (you never posted a gist), my assumption
would be you're doing a lot of copying between survivor generations, and
they're taking a long time.  You're probably also copying a lot of data to
your old gen as a result of having full-ish survivor spaces to begin with.

On Thu, Mar 3, 2016 at 10:26 PM Jeff Jirsa 
wrote:

> I’d personally would have gone the other way – if you’re seeing parnew,
> increasing new gen instead of decreasing it should help drop (faster)
> rather than promoting to sv/oldgen (slower) ?
>
>
>
> From: Anishek Agarwal
> Reply-To: "user@cassandra.apache.org"
> Date: Thursday, March 3, 2016 at 8:55 PM
>
> To: "user@cassandra.apache.org"
> Subject: Re: Lot of GC on two nodes out of 7
>
> Hello,
>
> Bryan, most of the partition sizes are under 45 KB
>
> I have tried with concurrent_compactors : 8 for one of the nodes still no
> improvement,
> I have tried max_heap_Size : 8G, no improvement.
>
> I will try the newHeapsize of 2G though i am sure CMS will be a longer
> then.
>
> Also doesn't look like i mentioned what type of GC was causing the
> problems. On both the nodes its the ParNewGC thats taking long for each run
> and too many runs are happening in succession.
>
> anishek
>
>
> On Fri, Mar 4, 2016 at 5:36 AM, Bryan Cheng  wrote:
>
>> Hi Anishek,
>>
>> In addition to the good advice others have given, do you notice any
>> abnormally large partitions? What does cfhistograms report for 99%
>> partition size? A few huge partitions will cause very disproportionate load
>> on your cluster, including high GC.
>>
>> --Bryan
>>
>> On Wed, Mar 2, 2016 at 9:28 AM, Amit Singh F 
>> wrote:
>>
>>> Hi Anishek,
>>>
>>>
>>>
>>> We too faced similar problem in 2.0.14 and after doing some research we
>>> config few parameters in Cassandra.yaml and was able to overcome GC pauses
>>> . Those are :
>>>
>>>
>>>
>>> · memtable_flush_writers : increased from 1 to 3 as from
>>> tpstats output  we can see mutations dropped so it means writes are getting
>>> blocked, so increasing number will have those catered.
>>>
>>> · memtable_total_space_in_mb : Default (1/4 of heap size), can
>>> lowered because larger long lived objects will create pressure on HEAP, so
>>> its better to reduce some amount of size.
>>>
>>> · Concurrent_compactors : Alain righlty pointed out this i.e
>>> reduce it to 8. You need to try this.
>>>
>>>
>>>
>>> Also please check whether you have mutations drop in other nodes or not.
>>>
>>>
>>>
>>> Hope this helps in your cluster too.
>>>
>>>
>>>
>>> Regards
>>>
>>> Amit Singh
>>>
>>> *From:* Jonathan Haddad [mailto:j...@jonhaddad.com]
>>> *Sent:* Wednesday, March 02, 2016 9:33 PM
>>> *To:* user@cassandra.apache.org
>>> *Subject:* Re: Lot of GC on two nodes out of 7
>>>
>>>
>>>
>>> Can you post a gist of the output of jstat -gccause (60 seconds worth)?
>>> I think it's cool you're willing to experiment with alternative JVM
>>> settings but I've never seen anyone use max tenuring threshold of 50 either
>>> and I can't imagine it's helpful.  Keep in mind if your objects are
>>> actually reaching that threshold it means they've been copied 50x (really
>>> really slow) and also you're going to end up spilling your eden objects
>>> directly into your old gen if your survivor is full.  Considering the small
>>> amount of memory you're using for heap I'm really not surprised you're
>>> running into problems.
>>>
>>>
>>>
>>> I recommend G1GC + 12GB heap and just let it optimize itself for almost
>>> all cases with the latest JVM versions.
>>>
>>>
>>>
>>> On Wed, Mar 2, 2016 at 6:08 AM Alain RODRIGUEZ 
>>> wrote:
>>>
>>> It looks like you are doing a good work with this cluster and know a lot
>>> about JVM, that's good :-).
>>>
>>>
>>>
>>> our machine configurations are : 2 X 800 GB SSD , 48 cores, 64 GB RAM
>>>
>>>
>>>
>>> That's good hardware too.
>>>
>>>
>>>
>>> With 64 GB of ram I would probably directly give a try to
>>> `MAX_HEAP_SIZE=8G` on one of the 2 bad nodes probably.
>>>
>>>
>>>
>>> Also I would also probably try lowering `HEAP_NEWSIZE=2G.` and using
>>> `-XX:MaxTenuringThreshold=15`, still on the canary node to observe the
>>> effects. But that's just an idea of something I would try to see the
>>> impacts, I don't think it will solve your current issues or even make it
>>> worse for this node.
>>>
>>>
>>>
>>> Using G1GC would allow you to use a bigger Heap size. Using C*2.1 would
>>> allow you to store the memtables off-heap. Those are 2 improvements
>>> reducing the heap pressure that you might be interested in.
>>>
>>>
>>>
>>> I have spent time reading about all other options before including them
>>> and a similar configuration on our other prod cluster is showing good GC
>>> graphs via gcviewer.
>>>
>>>
>>>
>>> So, let's look for an other reason.
>>>
>>>
>>>
>>> there are MUTATION and READ messages dropped in high number on nodes in

Re: Lot of GC on two nodes out of 7

[Jeff Jirsa]

I’d personally would have gone the other way – if you’re seeing parnew, 
increasing new gen instead of decreasing it should help drop (faster) rather 
than promoting to sv/oldgen (slower) ?



From:  Anishek Agarwal
Reply-To:  "user@cassandra.apache.org"
Date:  Thursday, March 3, 2016 at 8:55 PM
To:  "user@cassandra.apache.org"
Subject:  Re: Lot of GC on two nodes out of 7

Hello, 

Bryan, most of the partition sizes are under 45 KB

I have tried with concurrent_compactors : 8 for one of the nodes still no 
improvement, 
I have tried max_heap_Size : 8G, no improvement. 

I will try the newHeapsize of 2G though i am sure CMS will be a longer then.

Also doesn't look like i mentioned what type of GC was causing the problems. On 
both the nodes its the ParNewGC thats taking long for each run and too many 
runs are happening in succession. 

anishek


On Fri, Mar 4, 2016 at 5:36 AM, Bryan Cheng  wrote:
Hi Anishek, 

In addition to the good advice others have given, do you notice any abnormally 
large partitions? What does cfhistograms report for 99% partition size? A few 
huge partitions will cause very disproportionate load on your cluster, 
including high GC.

--Bryan

On Wed, Mar 2, 2016 at 9:28 AM, Amit Singh F  wrote:
Hi Anishek,

 

We too faced similar problem in 2.0.14 and after doing some research we config 
few parameters in Cassandra.yaml and was able to overcome GC pauses . Those are 
:

 

·memtable_flush_writers : increased from 1 to 3 as from tpstats output  
we can see mutations dropped so it means writes are getting blocked, so 
increasing number will have those catered.

·memtable_total_space_in_mb : Default (1/4 of heap size), can lowered 
because larger long lived objects will create pressure on HEAP, so its better 
to reduce some amount of size.

·Concurrent_compactors : Alain righlty pointed out this i.e reduce it 
to 8. You need to try this.

 

Also please check whether you have mutations drop in other nodes or not.

 

Hope this helps in your cluster too.

 

Regards

Amit Singh

From: Jonathan Haddad [mailto:j...@jonhaddad.com] 
Sent: Wednesday, March 02, 2016 9:33 PM
To: user@cassandra.apache.org
Subject: Re: Lot of GC on two nodes out of 7

 

Can you post a gist of the output of jstat -gccause (60 seconds worth)?  I 
think it's cool you're willing to experiment with alternative JVM settings but 
I've never seen anyone use max tenuring threshold of 50 either and I can't 
imagine it's helpful.  Keep in mind if your objects are actually reaching that 
threshold it means they've been copied 50x (really really slow) and also you're 
going to end up spilling your eden objects directly into your old gen if your 
survivor is full.  Considering the small amount of memory you're using for heap 
I'm really not surprised you're running into problems.  

 

I recommend G1GC + 12GB heap and just let it optimize itself for almost all 
cases with the latest JVM versions.

 

On Wed, Mar 2, 2016 at 6:08 AM Alain RODRIGUEZ  wrote:

It looks like you are doing a good work with this cluster and know a lot about 
JVM, that's good :-).

 

our machine configurations are : 2 X 800 GB SSD , 48 cores, 64 GB RAM

 

That's good hardware too.

 

With 64 GB of ram I would probably directly give a try to `MAX_HEAP_SIZE=8G` on 
one of the 2 bad nodes probably.

 

Also I would also probably try lowering `HEAP_NEWSIZE=2G.` and using 
`-XX:MaxTenuringThreshold=15`, still on the canary node to observe the effects. 
But that's just an idea of something I would try to see the impacts, I don't 
think it will solve your current issues or even make it worse for this node.

 

Using G1GC would allow you to use a bigger Heap size. Using C*2.1 would allow 
you to store the memtables off-heap. Those are 2 improvements reducing the heap 
pressure that you might be interested in.

 

I have spent time reading about all other options before including them and a 
similar configuration on our other prod cluster is showing good GC graphs via 
gcviewer.

 

So, let's look for an other reason. 

 

there are MUTATION and READ messages dropped in high number on nodes in 
question and on other 5 nodes it varies between 1-3.

 

- Is Memory, CPU or disk a bottleneck? Is one of those running at the limits?

 

concurrent_compactors: 48

 

Reducing this to 8 would free some space for transactions (R requests). It is 
probably worth a try, even more when compaction is not keeping up and 
compaction throughput is not throttled.

 

Just found an issue about that: 
https://issues.apache.org/jira/browse/CASSANDRA-7139

 

Looks like `concurrent_compactors: 8` is the new default.

 

C*heers,

---

Alain Rodriguez - al...@thelastpickle.com

France

 

The Last Pickle - Apache Cassandra Consulting

http://www.thelastpickle.com

 

 

 

 

 

 

2016-03-02 12:27 GMT+01:00 Anishek Agarwal :

Thanks a lot 

Re: Lot of GC on two nodes out of 7

[Anishek Agarwal]

Hello,

Bryan, most of the partition sizes are under 45 KB

I have tried with concurrent_compactors : 8 for one of the nodes still no
improvement,
I have tried max_heap_Size : 8G, no improvement.

I will try the newHeapsize of 2G though i am sure CMS will be a longer then.

Also doesn't look like i mentioned what type of GC was causing the
problems. On both the nodes its the ParNewGC thats taking long for each run
and too many runs are happening in succession.

anishek


On Fri, Mar 4, 2016 at 5:36 AM, Bryan Cheng  wrote:

> Hi Anishek,
>
> In addition to the good advice others have given, do you notice any
> abnormally large partitions? What does cfhistograms report for 99%
> partition size? A few huge partitions will cause very disproportionate load
> on your cluster, including high GC.
>
> --Bryan
>
> On Wed, Mar 2, 2016 at 9:28 AM, Amit Singh F 
> wrote:
>
>> Hi Anishek,
>>
>>
>>
>> We too faced similar problem in 2.0.14 and after doing some research we
>> config few parameters in Cassandra.yaml and was able to overcome GC pauses
>> . Those are :
>>
>>
>>
>> · memtable_flush_writers : increased from 1 to 3 as from tpstats
>> output  we can see mutations dropped so it means writes are getting
>> blocked, so increasing number will have those catered.
>>
>> · memtable_total_space_in_mb : Default (1/4 of heap size), can
>> lowered because larger long lived objects will create pressure on HEAP, so
>> its better to reduce some amount of size.
>>
>> · Concurrent_compactors : Alain righlty pointed out this i.e
>> reduce it to 8. You need to try this.
>>
>>
>>
>> Also please check whether you have mutations drop in other nodes or not.
>>
>>
>>
>> Hope this helps in your cluster too.
>>
>>
>>
>> Regards
>>
>> Amit Singh
>>
>> *From:* Jonathan Haddad [mailto:j...@jonhaddad.com]
>> *Sent:* Wednesday, March 02, 2016 9:33 PM
>> *To:* user@cassandra.apache.org
>> *Subject:* Re: Lot of GC on two nodes out of 7
>>
>>
>>
>> Can you post a gist of the output of jstat -gccause (60 seconds worth)?
>> I think it's cool you're willing to experiment with alternative JVM
>> settings but I've never seen anyone use max tenuring threshold of 50 either
>> and I can't imagine it's helpful.  Keep in mind if your objects are
>> actually reaching that threshold it means they've been copied 50x (really
>> really slow) and also you're going to end up spilling your eden objects
>> directly into your old gen if your survivor is full.  Considering the small
>> amount of memory you're using for heap I'm really not surprised you're
>> running into problems.
>>
>>
>>
>> I recommend G1GC + 12GB heap and just let it optimize itself for almost
>> all cases with the latest JVM versions.
>>
>>
>>
>> On Wed, Mar 2, 2016 at 6:08 AM Alain RODRIGUEZ 
>> wrote:
>>
>> It looks like you are doing a good work with this cluster and know a lot
>> about JVM, that's good :-).
>>
>>
>>
>> our machine configurations are : 2 X 800 GB SSD , 48 cores, 64 GB RAM
>>
>>
>>
>> That's good hardware too.
>>
>>
>>
>> With 64 GB of ram I would probably directly give a try to
>> `MAX_HEAP_SIZE=8G` on one of the 2 bad nodes probably.
>>
>>
>>
>> Also I would also probably try lowering `HEAP_NEWSIZE=2G.` and using
>> `-XX:MaxTenuringThreshold=15`, still on the canary node to observe the
>> effects. But that's just an idea of something I would try to see the
>> impacts, I don't think it will solve your current issues or even make it
>> worse for this node.
>>
>>
>>
>> Using G1GC would allow you to use a bigger Heap size. Using C*2.1 would
>> allow you to store the memtables off-heap. Those are 2 improvements
>> reducing the heap pressure that you might be interested in.
>>
>>
>>
>> I have spent time reading about all other options before including them
>> and a similar configuration on our other prod cluster is showing good GC
>> graphs via gcviewer.
>>
>>
>>
>> So, let's look for an other reason.
>>
>>
>>
>> there are MUTATION and READ messages dropped in high number on nodes in
>> question and on other 5 nodes it varies between 1-3.
>>
>>
>>
>> - Is Memory, CPU or disk a bottleneck? Is one of those running at the
>> limits?
>>
>>
>>
>> concurrent_compactors: 48
>>
>>
>>
>> Reducing this to 8 would free some space for transactions (R requests).
>> It is probably worth a try, even more when compaction is not keeping up and
>> compaction throughput is not throttled.
>>
>>
>>
>> Just found an issue about that:
>> https://issues.apache.org/jira/browse/CASSANDRA-7139
>>
>>
>>
>> Looks like `concurrent_compactors: 8` is the new default.
>>
>>
>>
>> C*heers,
>>
>> ---
>>
>> Alain Rodriguez - al...@thelastpickle.com
>>
>> France
>>
>>
>>
>> The Last Pickle - Apache Cassandra Consulting
>>
>> http://www.thelastpickle.com
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> 2016-03-02 12:27 GMT+01:00 Anishek Agarwal :
>>
>> Thanks a lot Alian for the details.
>>

Re: Lot of GC on two nodes out of 7

[Bryan Cheng]

Hi Anishek,

In addition to the good advice others have given, do you notice any
abnormally large partitions? What does cfhistograms report for 99%
partition size? A few huge partitions will cause very disproportionate load
on your cluster, including high GC.

--Bryan

On Wed, Mar 2, 2016 at 9:28 AM, Amit Singh F 
wrote:

> Hi Anishek,
>
>
>
> We too faced similar problem in 2.0.14 and after doing some research we
> config few parameters in Cassandra.yaml and was able to overcome GC pauses
> . Those are :
>
>
>
> · memtable_flush_writers : increased from 1 to 3 as from tpstats
> output  we can see mutations dropped so it means writes are getting
> blocked, so increasing number will have those catered.
>
> · memtable_total_space_in_mb : Default (1/4 of heap size), can
> lowered because larger long lived objects will create pressure on HEAP, so
> its better to reduce some amount of size.
>
> · Concurrent_compactors : Alain righlty pointed out this i.e
> reduce it to 8. You need to try this.
>
>
>
> Also please check whether you have mutations drop in other nodes or not.
>
>
>
> Hope this helps in your cluster too.
>
>
>
> Regards
>
> Amit Singh
>
> *From:* Jonathan Haddad [mailto:j...@jonhaddad.com]
> *Sent:* Wednesday, March 02, 2016 9:33 PM
> *To:* user@cassandra.apache.org
> *Subject:* Re: Lot of GC on two nodes out of 7
>
>
>
> Can you post a gist of the output of jstat -gccause (60 seconds worth)?  I
> think it's cool you're willing to experiment with alternative JVM settings
> but I've never seen anyone use max tenuring threshold of 50 either and I
> can't imagine it's helpful.  Keep in mind if your objects are actually
> reaching that threshold it means they've been copied 50x (really really
> slow) and also you're going to end up spilling your eden objects directly
> into your old gen if your survivor is full.  Considering the small amount
> of memory you're using for heap I'm really not surprised you're running
> into problems.
>
>
>
> I recommend G1GC + 12GB heap and just let it optimize itself for almost
> all cases with the latest JVM versions.
>
>
>
> On Wed, Mar 2, 2016 at 6:08 AM Alain RODRIGUEZ  wrote:
>
> It looks like you are doing a good work with this cluster and know a lot
> about JVM, that's good :-).
>
>
>
> our machine configurations are : 2 X 800 GB SSD , 48 cores, 64 GB RAM
>
>
>
> That's good hardware too.
>
>
>
> With 64 GB of ram I would probably directly give a try to
> `MAX_HEAP_SIZE=8G` on one of the 2 bad nodes probably.
>
>
>
> Also I would also probably try lowering `HEAP_NEWSIZE=2G.` and using
> `-XX:MaxTenuringThreshold=15`, still on the canary node to observe the
> effects. But that's just an idea of something I would try to see the
> impacts, I don't think it will solve your current issues or even make it
> worse for this node.
>
>
>
> Using G1GC would allow you to use a bigger Heap size. Using C*2.1 would
> allow you to store the memtables off-heap. Those are 2 improvements
> reducing the heap pressure that you might be interested in.
>
>
>
> I have spent time reading about all other options before including them
> and a similar configuration on our other prod cluster is showing good GC
> graphs via gcviewer.
>
>
>
> So, let's look for an other reason.
>
>
>
> there are MUTATION and READ messages dropped in high number on nodes in
> question and on other 5 nodes it varies between 1-3.
>
>
>
> - Is Memory, CPU or disk a bottleneck? Is one of those running at the
> limits?
>
>
>
> concurrent_compactors: 48
>
>
>
> Reducing this to 8 would free some space for transactions (R requests).
> It is probably worth a try, even more when compaction is not keeping up and
> compaction throughput is not throttled.
>
>
>
> Just found an issue about that:
> https://issues.apache.org/jira/browse/CASSANDRA-7139
>
>
>
> Looks like `concurrent_compactors: 8` is the new default.
>
>
>
> C*heers,
>
> ---
>
> Alain Rodriguez - al...@thelastpickle.com
>
> France
>
>
>
> The Last Pickle - Apache Cassandra Consulting
>
> http://www.thelastpickle.com
>
>
>
>
>
>
>
>
>
>
>
>
>
> 2016-03-02 12:27 GMT+01:00 Anishek Agarwal :
>
> Thanks a lot Alian for the details.
>
> `HEAP_NEWSIZE=4G.` is probably far too high (try 1200M <-> 2G)
> `MAX_HEAP_SIZE=6G` might be too low, how much memory is available (You
> might want to keep this as it or even reduce it if you have less than 16 GB
> of native memory. Go with 8 GB if you have a lot of memory.
> `-XX:MaxTenuringThreshold=50` is the highest value I have seen in use so
> far. I had luck with values between 4 <--> 16 in the past. I would give  a
> try with 15.
> `-XX:CMSInitiatingOccupancyFraction=70`--> Why not using default - 75 ?
> Using default and then tune from there to improve things is generally a
> good idea.
>
>
>
>
>
> we have a lot of reads and writes onto the system so keeping the high new
> size to make sure enough is held in memory 

RE: Lot of GC on two nodes out of 7

[Amit Singh F]

Hi Anishek,

We too faced similar problem in 2.0.14 and after doing some research we config 
few parameters in Cassandra.yaml and was able to overcome GC pauses . Those are 
:


· memtable_flush_writers : increased from 1 to 3 as from tpstats output 
 we can see mutations dropped so it means writes are getting blocked, so 
increasing number will have those catered.

· memtable_total_space_in_mb : Default (1/4 of heap size), can lowered 
because larger long lived objects will create pressure on HEAP, so its better 
to reduce some amount of size.

· Concurrent_compactors : Alain righlty pointed out this i.e reduce it 
to 8. You need to try this.

Also please check whether you have mutations drop in other nodes or not.

Hope this helps in your cluster too.

Regards
Amit Singh
From: Jonathan Haddad [mailto:j...@jonhaddad.com]
Sent: Wednesday, March 02, 2016 9:33 PM
To: user@cassandra.apache.org
Subject: Re: Lot of GC on two nodes out of 7

Can you post a gist of the output of jstat -gccause (60 seconds worth)?  I 
think it's cool you're willing to experiment with alternative JVM settings but 
I've never seen anyone use max tenuring threshold of 50 either and I can't 
imagine it's helpful.  Keep in mind if your objects are actually reaching that 
threshold it means they've been copied 50x (really really slow) and also you're 
going to end up spilling your eden objects directly into your old gen if your 
survivor is full.  Considering the small amount of memory you're using for heap 
I'm really not surprised you're running into problems.

I recommend G1GC + 12GB heap and just let it optimize itself for almost all 
cases with the latest JVM versions.

On Wed, Mar 2, 2016 at 6:08 AM Alain RODRIGUEZ 
> wrote:
It looks like you are doing a good work with this cluster and know a lot about 
JVM, that's good :-).

our machine configurations are : 2 X 800 GB SSD , 48 cores, 64 GB RAM

That's good hardware too.

With 64 GB of ram I would probably directly give a try to `MAX_HEAP_SIZE=8G` on 
one of the 2 bad nodes probably.

Also I would also probably try lowering `HEAP_NEWSIZE=2G.` and using 
`-XX:MaxTenuringThreshold=15`, still on the canary node to observe the effects. 
But that's just an idea of something I would try to see the impacts, I don't 
think it will solve your current issues or even make it worse for this node.

Using G1GC would allow you to use a bigger Heap size. Using C*2.1 would allow 
you to store the memtables off-heap. Those are 2 improvements reducing the heap 
pressure that you might be interested in.

I have spent time reading about all other options before including them and a 
similar configuration on our other prod cluster is showing good GC graphs via 
gcviewer.

So, let's look for an other reason.

there are MUTATION and READ messages dropped in high number on nodes in 
question and on other 5 nodes it varies between 1-3.

- Is Memory, CPU or disk a bottleneck? Is one of those running at the limits?

concurrent_compactors: 48

Reducing this to 8 would free some space for transactions (R requests). It is 
probably worth a try, even more when compaction is not keeping up and 
compaction throughput is not throttled.

Just found an issue about that: 
https://issues.apache.org/jira/browse/CASSANDRA-7139

Looks like `concurrent_compactors: 8` is the new default.

C*heers,
---
Alain Rodriguez - al...@thelastpickle.com
France

The Last Pickle - Apache Cassandra Consulting
http://www.thelastpickle.com






2016-03-02 12:27 GMT+01:00 Anishek Agarwal 
>:
Thanks a lot Alian for the details.
`HEAP_NEWSIZE=4G.` is probably far too high (try 1200M <-> 2G)
`MAX_HEAP_SIZE=6G` might be too low, how much memory is available (You might 
want to keep this as it or even reduce it if you have less than 16 GB of native 
memory. Go with 8 GB if you have a lot of memory.
`-XX:MaxTenuringThreshold=50` is the highest value I have seen in use so far. I 
had luck with values between 4 <--> 16 in the past. I would give  a try with 15.
`-XX:CMSInitiatingOccupancyFraction=70`--> Why not using default - 75 ? Using 
default and then tune from there to improve things is generally a good idea.


we have a lot of reads and writes onto the system so keeping the high new size 
to make sure enough is held in memory including caches / memtables etc --number 
of flush_writers : 4 for us. similarly keeping less in old generation to make 
sure we spend less time with CMS GC most of the data is transient in memory for 
us. Keeping high TenuringThreshold because we don't want objects going to old 
generation and just die in young generation given we have configured large 
survivor spaces.
using occupancyFraction as 70 since
given heap is 4G
survivor space is : 400 mb -- 2 survivor spaces
70 % of 2G (old generation) = 1.4G

so once we are just below 1.4G and we have to move 

RE: Lot of GC on two nodes out of 7

[Amit Singh F]

Hi Anishek,

We too faced similar problem in 2.0.14 and after doing some research we config 
few parameters in Cassandra.yaml and was able to overcome GC pauses . Those are 
:


· memtable_flush_writers : increased from 1 to 3 as from tpstats output 
 we can see mutations dropped so it means writes are getting blocked, so 
increasing number will have those catered.

· memtable_total_space_in_mb : Default (1/4 of heap size), can lowered 
because larger long lived objects will create pressure on HEAP, so its better 
to reduce some amount of size.

· Concurrent_compactors : Alain righlty pointed out this i.e reduce it 
to 8. You need to try this.

Also please check whether you have mutations drop in other nodes or not.

Hope this helps in your cluster too.

Regards
Amit Singh

From: Jonathan Haddad [mailto:j...@jonhaddad.com]
Sent: Wednesday, March 02, 2016 9:33 PM
To: user@cassandra.apache.org
Subject: Re: Lot of GC on two nodes out of 7

Can you post a gist of the output of jstat -gccause (60 seconds worth)?  I 
think it's cool you're willing to experiment with alternative JVM settings but 
I've never seen anyone use max tenuring threshold of 50 either and I can't 
imagine it's helpful.  Keep in mind if your objects are actually reaching that 
threshold it means they've been copied 50x (really really slow) and also you're 
going to end up spilling your eden objects directly into your old gen if your 
survivor is full.  Considering the small amount of memory you're using for heap 
I'm really not surprised you're running into problems.

I recommend G1GC + 12GB heap and just let it optimize itself for almost all 
cases with the latest JVM versions.

On Wed, Mar 2, 2016 at 6:08 AM Alain RODRIGUEZ 
> wrote:
It looks like you are doing a good work with this cluster and know a lot about 
JVM, that's good :-).

our machine configurations are : 2 X 800 GB SSD , 48 cores, 64 GB RAM

That's good hardware too.

With 64 GB of ram I would probably directly give a try to `MAX_HEAP_SIZE=8G` on 
one of the 2 bad nodes probably.

Also I would also probably try lowering `HEAP_NEWSIZE=2G.` and using 
`-XX:MaxTenuringThreshold=15`, still on the canary node to observe the effects. 
But that's just an idea of something I would try to see the impacts, I don't 
think it will solve your current issues or even make it worse for this node.

Using G1GC would allow you to use a bigger Heap size. Using C*2.1 would allow 
you to store the memtables off-heap. Those are 2 improvements reducing the heap 
pressure that you might be interested in.

I have spent time reading about all other options before including them and a 
similar configuration on our other prod cluster is showing good GC graphs via 
gcviewer.

So, let's look for an other reason.

there are MUTATION and READ messages dropped in high number on nodes in 
question and on other 5 nodes it varies between 1-3.

- Is Memory, CPU or disk a bottleneck? Is one of those running at the limits?

concurrent_compactors: 48

Reducing this to 8 would free some space for transactions (R requests). It is 
probably worth a try, even more when compaction is not keeping up and 
compaction throughput is not throttled.

Just found an issue about that: 
https://issues.apache.org/jira/browse/CASSANDRA-7139

Looks like `concurrent_compactors: 8` is the new default.

C*heers,
---
Alain Rodriguez - al...@thelastpickle.com
France

The Last Pickle - Apache Cassandra Consulting
http://www.thelastpickle.com






2016-03-02 12:27 GMT+01:00 Anishek Agarwal 
>:
Thanks a lot Alian for the details.
`HEAP_NEWSIZE=4G.` is probably far too high (try 1200M <-> 2G)
`MAX_HEAP_SIZE=6G` might be too low, how much memory is available (You might 
want to keep this as it or even reduce it if you have less than 16 GB of native 
memory. Go with 8 GB if you have a lot of memory.
`-XX:MaxTenuringThreshold=50` is the highest value I have seen in use so far. I 
had luck with values between 4 <--> 16 in the past. I would give  a try with 15.
`-XX:CMSInitiatingOccupancyFraction=70`--> Why not using default - 75 ? Using 
default and then tune from there to improve things is generally a good idea.


we have a lot of reads and writes onto the system so keeping the high new size 
to make sure enough is held in memory including caches / memtables etc --number 
of flush_writers : 4 for us. similarly keeping less in old generation to make 
sure we spend less time with CMS GC most of the data is transient in memory for 
us. Keeping high TenuringThreshold because we don't want objects going to old 
generation and just die in young generation given we have configured large 
survivor spaces.
using occupancyFraction as 70 since
given heap is 4G
survivor space is : 400 mb -- 2 survivor spaces
70 % of 2G (old generation) = 1.4G

so once we are 

Re: Lot of GC on two nodes out of 7

[Alain RODRIGUEZ]

It looks like you are doing a good work with this cluster and know a lot
about JVM, that's good :-).

our machine configurations are : 2 X 800 GB SSD , 48 cores, 64 GB RAM


That's good hardware too.

With 64 GB of ram I would probably directly give a try to
`MAX_HEAP_SIZE=8G` on one of the 2 bad nodes probably.

Also I would also probably try lowering `HEAP_NEWSIZE=2G.` and using
`-XX:MaxTenuringThreshold=15`, still on the canary node to observe the
effects. But that's just an idea of something I would try to see the
impacts, I don't think it will solve your current issues or even make it
worse for this node.

Using G1GC would allow you to use a bigger Heap size. Using C*2.1 would
allow you to store the memtables off-heap. Those are 2 improvements
reducing the heap pressure that you might be interested in.

I have spent time reading about all other options before including them and
> a similar configuration on our other prod cluster is showing good GC graphs
> via gcviewer.


So, let's look for an other reason.

there are MUTATION and READ messages dropped in high number on nodes in
> question and on other 5 nodes it varies between 1-3.


- Is Memory, CPU or disk a bottleneck? Is one of those running at the
limits?

concurrent_compactors: 48


Reducing this to 8 would free some space for transactions (R requests).
It is probably worth a try, even more when compaction is not keeping up and
compaction throughput is not throttled.

Just found an issue about that:
https://issues.apache.org/jira/browse/CASSANDRA-7139

Looks like `concurrent_compactors: 8` is the new default.

C*heers,
---
Alain Rodriguez - al...@thelastpickle.com
France

The Last Pickle - Apache Cassandra Consulting
http://www.thelastpickle.com






2016-03-02 12:27 GMT+01:00 Anishek Agarwal :

> Thanks a lot Alian for the details.
>
>> `HEAP_NEWSIZE=4G.` is probably far too high (try 1200M <-> 2G)
>> `MAX_HEAP_SIZE=6G` might be too low, how much memory is available (You
>> might want to keep this as it or even reduce it if you have less than 16 GB
>> of native memory. Go with 8 GB if you have a lot of memory.
>> `-XX:MaxTenuringThreshold=50` is the highest value I have seen in use so
>> far. I had luck with values between 4 <--> 16 in the past. I would give  a
>> try with 15.
>> `-XX:CMSInitiatingOccupancyFraction=70`--> Why not using default - 75 ?
>> Using default and then tune from there to improve things is generally a
>> good idea.
>
>
>
> we have a lot of reads and writes onto the system so keeping the high new
> size to make sure enough is held in memory including caches / memtables etc
> --number of flush_writers : 4 for us. similarly keeping less in old
> generation to make sure we spend less time with CMS GC most of the data is
> transient in memory for us. Keeping high TenuringThreshold because we don't
> want objects going to old generation and just die in young generation given
> we have configured large survivor spaces.
> using occupancyFraction as 70 since
> given heap is 4G
> survivor space is : 400 mb -- 2 survivor spaces
> 70 % of 2G (old generation) = 1.4G
>
> so once we are just below 1.4G and we have to move the full survivor +
> some extra during a par new gc due to promotion failure, everything will
> fit in old generation, and will trigger CMS.
>
> I have spent time reading about all other options before including them
> and a similar configuration on our other prod cluster is showing good GC
> graphs via gcviewer.
>
> tp stats on all machines show flush writer blocked at : 0.3% of total
>
> the two nodes in question have stats almost as below
>
>- specifically there are pending was in readStage, MutationStage and
>RequestResponseStage
>
> Pool NameActive   Pending  Completed   Blocked
> All time blocked
>
> ReadStage2119 2141798645 0
> 0
>
> RequestResponseStage  0 1  803242391 0
> 0
>
> MutationStage 0 0  291813703 0
> 0
>
> ReadRepairStage   0 0  200544344 0
> 0
>
> ReplicateOnWriteStage 0 0  0 0
> 0
>
> GossipStage   0 0 292477 0
> 0
>
> CacheCleanupExecutor  0 0  0 0
> 0
>
> MigrationStage0 0  0 0
> 0
>
> MemoryMeter   0 0   2172 0
> 0
>
> FlushWriter   0 0   2756 0
> 6
>
> ValidationExecutor0 0101 0
> 0
>
> InternalResponseStage 0 0  0 0
> 0
>
> AntiEntropyStage  0 0202 

Re: Lot of GC on two nodes out of 7

[Anishek Agarwal]

Thanks a lot Alian for the details.

> `HEAP_NEWSIZE=4G.` is probably far too high (try 1200M <-> 2G)
> `MAX_HEAP_SIZE=6G` might be too low, how much memory is available (You
> might want to keep this as it or even reduce it if you have less than 16 GB
> of native memory. Go with 8 GB if you have a lot of memory.
> `-XX:MaxTenuringThreshold=50` is the highest value I have seen in use so
> far. I had luck with values between 4 <--> 16 in the past. I would give  a
> try with 15.
> `-XX:CMSInitiatingOccupancyFraction=70`--> Why not using default - 75 ?
> Using default and then tune from there to improve things is generally a
> good idea.



we have a lot of reads and writes onto the system so keeping the high new
size to make sure enough is held in memory including caches / memtables etc
--number of flush_writers : 4 for us. similarly keeping less in old
generation to make sure we spend less time with CMS GC most of the data is
transient in memory for us. Keeping high TenuringThreshold because we don't
want objects going to old generation and just die in young generation given
we have configured large survivor spaces.
using occupancyFraction as 70 since
given heap is 4G
survivor space is : 400 mb -- 2 survivor spaces
70 % of 2G (old generation) = 1.4G

so once we are just below 1.4G and we have to move the full survivor + some
extra during a par new gc due to promotion failure, everything will fit in
old generation, and will trigger CMS.

I have spent time reading about all other options before including them and
a similar configuration on our other prod cluster is showing good GC graphs
via gcviewer.

tp stats on all machines show flush writer blocked at : 0.3% of total

the two nodes in question have stats almost as below

   - specifically there are pending was in readStage, MutationStage and
   RequestResponseStage

Pool NameActive   Pending  Completed   Blocked  All
time blocked

ReadStage2119 2141798645 0
0

RequestResponseStage  0 1  803242391 0
0

MutationStage 0 0  291813703 0
0

ReadRepairStage   0 0  200544344 0
0

ReplicateOnWriteStage 0 0  0 0
0

GossipStage   0 0 292477 0
0

CacheCleanupExecutor  0 0  0 0
0

MigrationStage0 0  0 0
0

MemoryMeter   0 0   2172 0
0

FlushWriter   0 0   2756 0
6

ValidationExecutor0 0101 0
0

InternalResponseStage 0 0  0 0
0

AntiEntropyStage  0 0202 0
0

MemtablePostFlusher   0 0   4395 0
0

MiscStage 0 0  0 0
0

PendingRangeCalculator0 0 20 0
0

CompactionExecutor4 4  49323 0
0

commitlog_archiver0 0  0 0
0

HintedHandoff 0 0116 0
0


Message type   Dropped

RANGE_SLICE  0

READ_REPAIR 36

PAGED_RANGE  0

BINARY   0

READ 11471

MUTATION   898

_TRACE   0

REQUEST_RESPONSE 0

COUNTER_MUTATION 0

all the other 5 nodes show no pending numbers.


our machine configurations are : 2 X 800 GB SSD , 48 cores, 64 GB RAM
compaction throughput is 0 MB/s
concurrent_compactors: 48
flush_writers: 4


> I think Jeff is trying to spot a wide row messing with your system, so
> looking at the max row size on those nodes compared to other is more
> relevant than average size for this check.


i think is what you are looking for, please correct me if i am wrong

Compacted partition maximum bytes: 1629722
similar value on all 7 nodes.

grep -i "ERROR" /var/log/cassandra/system.log


there are MUTATION and READ messages dropped in high number on nodes in
question and on other 5 nodes it varies between 1-3.

On Wed, Mar 2, 2016 at 4:15 PM, Alain RODRIGUEZ  wrote:

> Hi Anishek,
>
> Even if it highly depends on your workload, here are my thoughts:
>
> `HEAP_NEWSIZE=4G.` is probably far too high (try 1200M <-> 2G)
> `MAX_HEAP_SIZE=6G` might be too low, how much memory is available (You
> might want to keep this as it or even reduce it if you have less than 16 GB
> of native memory. 

Re: Lot of GC on two nodes out of 7

[Alain RODRIGUEZ]

Hi Anishek,

Even if it highly depends on your workload, here are my thoughts:

`HEAP_NEWSIZE=4G.` is probably far too high (try 1200M <-> 2G)
`MAX_HEAP_SIZE=6G` might be too low, how much memory is available (You
might want to keep this as it or even reduce it if you have less than 16 GB
of native memory. Go with 8 GB if you have a lot of memory.
`-XX:MaxTenuringThreshold=50` is the highest value I have seen in use so
far. I had luck with values between 4 <--> 16 in the past. I would give  a
try with 15.
`-XX:CMSInitiatingOccupancyFraction=70`--> Why not using default - 75 ?
Using default and then tune from there to improve things is generally a
good idea.

You also use a bunch of option I don't know about, if you are uncertain
about them, you could try a default conf without the options you added and
just the using the changes above from default
https://github.com/apache/cassandra/blob/cassandra-2.0/conf/cassandra-env.sh.
Or you might find more useful information on a nice reference about this
topic which is Al Tobey's blog post about tuning 2.1. Go to the 'Java
Virtual Machine' part:
https://tobert.github.io/pages/als-cassandra-21-tuning-guide.html

FWIW, I also saw improvement in the past by upgrading to 2.1, Java 8 and
G1GC. G1GC is supposed to be easier to configure too.

the average row size for compacted partitions is about 1640 bytes on all
> nodes. We have replication factor 3 but the problem is only on two nodes.
>

I think Jeff is trying to spot a wide row messing with your system, so
looking at the max row size on those nodes compared to other is more
relevant than average size for this check.

the only other thing that stands out in cfstats is the read time and write
> time on the nodes with high GC is 5-7 times higher than other 5 nodes, but
> i think thats expected.


I would probably look at this the reverse way: I imagine that extra GC  is
a consequence of something going wrong on those nodes as JVM / GC are
configured the same way cluster-wide. GC / JVM issues are often due to
Cassandra / system / hardware issues, inducing extra pressure on the JVM. I
would try to tune JVM / GC only once the system is healthy. So I often saw
high GC being a consequence rather than the root cause of an issue.

To explore this possibility:

Does this command show some dropped or blocked tasks? This would add
pressure to heap.
nodetool tpstats

Do you have errors in logs? Always good to know when facing an issue.
grep -i "ERROR" /var/log/cassandra/system.log

How are compactions tuned (throughput + concurrent compactors)? This tuning
might explain compactions not keeping up or a high GC pressure.

What are your disks / CPU? To help us giving you good arbitrary values to
try.

Is there some iowait ? Could point to a bottleneck or bad hardware.
iostats -mx 5 100

...

Hope one of those will point you to an issue, but there are many more thing
you could check.

Let us know how it goes,

C*heers,
---
Alain Rodriguez - al...@thelastpickle.com
France

The Last Pickle - Apache Cassandra Consulting
http://www.thelastpickle.com



2016-03-02 10:33 GMT+01:00 Anishek Agarwal :

> also MAX_HEAP_SIZE=6G and HEAP_NEWSIZE=4G.
>
> On Wed, Mar 2, 2016 at 1:40 PM, Anishek Agarwal  wrote:
>
>> Hey Jeff,
>>
>> one of the nodes with high GC has 1400 SST tables, all other nodes have
>> about 500-900 SST tables. the other node with high GC has 636 SST tables.
>>
>> the average row size for compacted partitions is about 1640 bytes on all
>> nodes. We have replication factor 3 but the problem is only on two nodes.
>> the only other thing that stands out in cfstats is the read time and
>> write time on the nodes with high GC is 5-7 times higher than other 5
>> nodes, but i think thats expected.
>>
>> thanks
>> anishek
>>
>>
>>
>>
>> On Wed, Mar 2, 2016 at 1:09 PM, Jeff Jirsa 
>> wrote:
>>
>>> Compaction falling behind will likely cause additional work on reads
>>> (more sstables to merge), but I’d be surprised if it manifested in super
>>> long GC. When you say twice as many sstables, how many is that?.
>>>
>>> In cfstats, does anything stand out? Is max row size on those nodes
>>> larger than on other nodes?
>>>
>>> What you don’t show in your JVM options is the new gen size – if you do
>>> have unusually large partitions on those two nodes (especially likely if
>>> you have rf=2 – if you have rf=3, then there’s probably a third node
>>> misbehaving you haven’t found yet), then raising new gen size can help
>>> handle the garbage created by reading large partitions without having to
>>> tolerate the promotion. Estimates for the amount of garbage vary, but it
>>> could be “gigabytes” of garbage on a very wide partition (see
>>> https://issues.apache.org/jira/browse/CASSANDRA-9754 for work in
>>> progress to help mitigate that type of pain).
>>>
>>> - Jeff
>>>
>>> From: Anishek Agarwal
>>> Reply-To: "user@cassandra.apache.org"
>>> Date: Tuesday, 

Re: Lot of GC on two nodes out of 7

[Anishek Agarwal]

also MAX_HEAP_SIZE=6G and HEAP_NEWSIZE=4G.

On Wed, Mar 2, 2016 at 1:40 PM, Anishek Agarwal  wrote:

> Hey Jeff,
>
> one of the nodes with high GC has 1400 SST tables, all other nodes have
> about 500-900 SST tables. the other node with high GC has 636 SST tables.
>
> the average row size for compacted partitions is about 1640 bytes on all
> nodes. We have replication factor 3 but the problem is only on two nodes.
> the only other thing that stands out in cfstats is the read time and write
> time on the nodes with high GC is 5-7 times higher than other 5 nodes, but
> i think thats expected.
>
> thanks
> anishek
>
>
>
>
> On Wed, Mar 2, 2016 at 1:09 PM, Jeff Jirsa 
> wrote:
>
>> Compaction falling behind will likely cause additional work on reads
>> (more sstables to merge), but I’d be surprised if it manifested in super
>> long GC. When you say twice as many sstables, how many is that?.
>>
>> In cfstats, does anything stand out? Is max row size on those nodes
>> larger than on other nodes?
>>
>> What you don’t show in your JVM options is the new gen size – if you do
>> have unusually large partitions on those two nodes (especially likely if
>> you have rf=2 – if you have rf=3, then there’s probably a third node
>> misbehaving you haven’t found yet), then raising new gen size can help
>> handle the garbage created by reading large partitions without having to
>> tolerate the promotion. Estimates for the amount of garbage vary, but it
>> could be “gigabytes” of garbage on a very wide partition (see
>> https://issues.apache.org/jira/browse/CASSANDRA-9754 for work in
>> progress to help mitigate that type of pain).
>>
>> - Jeff
>>
>> From: Anishek Agarwal
>> Reply-To: "user@cassandra.apache.org"
>> Date: Tuesday, March 1, 2016 at 11:12 PM
>> To: "user@cassandra.apache.org"
>> Subject: Lot of GC on two nodes out of 7
>>
>> Hello,
>>
>> we have a cassandra cluster of 7 nodes, all of them have the same JVM GC
>> configurations, all our writes /  reads use the TokenAware Policy wrapping
>> a DCAware policy. All nodes are part of same Datacenter.
>>
>> We are seeing that two nodes are having high GC collection times. Then
>> mostly seem to spend time in GC like about 300-600 ms. This also seems to
>> result in higher CPU utilisation on these machines. Other  5 nodes don't
>> have this problem.
>>
>> There is no additional repair activity going on the cluster, we are not
>> sure why this is happening.
>> we checked cfhistograms on the two CF we have in the cluster and number
>> of reads seems to be almost same.
>>
>> we also used cfstats to see the number of ssttables on each node and one
>> of the nodes with the above problem has twice the number of ssttables than
>> other nodes. This still doesnot explain why two nodes have high GC
>> Overheads. our GC config is as below:
>>
>> JVM_OPTS="$JVM_OPTS -XX:+UseParNewGC"
>>
>> JVM_OPTS="$JVM_OPTS -XX:+UseConcMarkSweepGC"
>>
>> JVM_OPTS="$JVM_OPTS -XX:+CMSParallelRemarkEnabled"
>>
>> JVM_OPTS="$JVM_OPTS -XX:SurvivorRatio=8"
>>
>> JVM_OPTS="$JVM_OPTS -XX:MaxTenuringThreshold=50"
>>
>> JVM_OPTS="$JVM_OPTS -XX:CMSInitiatingOccupancyFraction=70"
>>
>> JVM_OPTS="$JVM_OPTS -XX:+UseCMSInitiatingOccupancyOnly"
>>
>> JVM_OPTS="$JVM_OPTS -XX:+UseTLAB"
>>
>> JVM_OPTS="$JVM_OPTS -XX:MaxPermSize=256m"
>>
>> JVM_OPTS="$JVM_OPTS -XX:+AggressiveOpts"
>>
>> JVM_OPTS="$JVM_OPTS -XX:+UseCompressedOops"
>>
>> JVM_OPTS="$JVM_OPTS -XX:+CMSScavengeBeforeRemark"
>>
>> JVM_OPTS="$JVM_OPTS -XX:ConcGCThreads=48"
>>
>> JVM_OPTS="$JVM_OPTS -XX:ParallelGCThreads=48"
>>
>> JVM_OPTS="$JVM_OPTS -XX:-ExplicitGCInvokesConcurrent"
>>
>> JVM_OPTS="$JVM_OPTS -XX:+UnlockDiagnosticVMOptions"
>>
>> JVM_OPTS="$JVM_OPTS -XX:+UseGCTaskAffinity"
>>
>> JVM_OPTS="$JVM_OPTS -XX:+BindGCTaskThreadsToCPUs"
>>
>> # earlier value 131072 = 32768 * 4
>>
>> JVM_OPTS="$JVM_OPTS -XX:ParGCCardsPerStrideChunk=131072"
>>
>> JVM_OPTS="$JVM_OPTS -XX:CMSScheduleRemarkEdenSizeThreshold=104857600"
>>
>> JVM_OPTS="$JVM_OPTS -XX:CMSRescanMultiple=32768"
>>
>> JVM_OPTS="$JVM_OPTS -XX:CMSConcMarkMultiple=32768"
>>
>> #new
>>
>> JVM_OPTS="$JVM_OPTS -XX:+CMSConcurrentMTEnabled"
>>
>> We are using cassandra 2.0.17. If anyone has any suggestion as to how
>> what else we can look for to understand why this is happening please do
>> reply.
>>
>>
>>
>> Thanks
>> anishek
>>
>>
>>
>

Re: Lot of GC on two nodes out of 7

[Anishek Agarwal]

Hey Jeff,

one of the nodes with high GC has 1400 SST tables, all other nodes have
about 500-900 SST tables. the other node with high GC has 636 SST tables.

the average row size for compacted partitions is about 1640 bytes on all
nodes. We have replication factor 3 but the problem is only on two nodes.
the only other thing that stands out in cfstats is the read time and write
time on the nodes with high GC is 5-7 times higher than other 5 nodes, but
i think thats expected.

thanks
anishek




On Wed, Mar 2, 2016 at 1:09 PM, Jeff Jirsa 
wrote:

> Compaction falling behind will likely cause additional work on reads (more
> sstables to merge), but I’d be surprised if it manifested in super long GC.
> When you say twice as many sstables, how many is that?.
>
> In cfstats, does anything stand out? Is max row size on those nodes larger
> than on other nodes?
>
> What you don’t show in your JVM options is the new gen size – if you do
> have unusually large partitions on those two nodes (especially likely if
> you have rf=2 – if you have rf=3, then there’s probably a third node
> misbehaving you haven’t found yet), then raising new gen size can help
> handle the garbage created by reading large partitions without having to
> tolerate the promotion. Estimates for the amount of garbage vary, but it
> could be “gigabytes” of garbage on a very wide partition (see
> https://issues.apache.org/jira/browse/CASSANDRA-9754 for work in progress
> to help mitigate that type of pain).
>
> - Jeff
>
> From: Anishek Agarwal
> Reply-To: "user@cassandra.apache.org"
> Date: Tuesday, March 1, 2016 at 11:12 PM
> To: "user@cassandra.apache.org"
> Subject: Lot of GC on two nodes out of 7
>
> Hello,
>
> we have a cassandra cluster of 7 nodes, all of them have the same JVM GC
> configurations, all our writes /  reads use the TokenAware Policy wrapping
> a DCAware policy. All nodes are part of same Datacenter.
>
> We are seeing that two nodes are having high GC collection times. Then
> mostly seem to spend time in GC like about 300-600 ms. This also seems to
> result in higher CPU utilisation on these machines. Other  5 nodes don't
> have this problem.
>
> There is no additional repair activity going on the cluster, we are not
> sure why this is happening.
> we checked cfhistograms on the two CF we have in the cluster and number of
> reads seems to be almost same.
>
> we also used cfstats to see the number of ssttables on each node and one
> of the nodes with the above problem has twice the number of ssttables than
> other nodes. This still doesnot explain why two nodes have high GC
> Overheads. our GC config is as below:
>
> JVM_OPTS="$JVM_OPTS -XX:+UseParNewGC"
>
> JVM_OPTS="$JVM_OPTS -XX:+UseConcMarkSweepGC"
>
> JVM_OPTS="$JVM_OPTS -XX:+CMSParallelRemarkEnabled"
>
> JVM_OPTS="$JVM_OPTS -XX:SurvivorRatio=8"
>
> JVM_OPTS="$JVM_OPTS -XX:MaxTenuringThreshold=50"
>
> JVM_OPTS="$JVM_OPTS -XX:CMSInitiatingOccupancyFraction=70"
>
> JVM_OPTS="$JVM_OPTS -XX:+UseCMSInitiatingOccupancyOnly"
>
> JVM_OPTS="$JVM_OPTS -XX:+UseTLAB"
>
> JVM_OPTS="$JVM_OPTS -XX:MaxPermSize=256m"
>
> JVM_OPTS="$JVM_OPTS -XX:+AggressiveOpts"
>
> JVM_OPTS="$JVM_OPTS -XX:+UseCompressedOops"
>
> JVM_OPTS="$JVM_OPTS -XX:+CMSScavengeBeforeRemark"
>
> JVM_OPTS="$JVM_OPTS -XX:ConcGCThreads=48"
>
> JVM_OPTS="$JVM_OPTS -XX:ParallelGCThreads=48"
>
> JVM_OPTS="$JVM_OPTS -XX:-ExplicitGCInvokesConcurrent"
>
> JVM_OPTS="$JVM_OPTS -XX:+UnlockDiagnosticVMOptions"
>
> JVM_OPTS="$JVM_OPTS -XX:+UseGCTaskAffinity"
>
> JVM_OPTS="$JVM_OPTS -XX:+BindGCTaskThreadsToCPUs"
>
> # earlier value 131072 = 32768 * 4
>
> JVM_OPTS="$JVM_OPTS -XX:ParGCCardsPerStrideChunk=131072"
>
> JVM_OPTS="$JVM_OPTS -XX:CMSScheduleRemarkEdenSizeThreshold=104857600"
>
> JVM_OPTS="$JVM_OPTS -XX:CMSRescanMultiple=32768"
>
> JVM_OPTS="$JVM_OPTS -XX:CMSConcMarkMultiple=32768"
>
> #new
>
> JVM_OPTS="$JVM_OPTS -XX:+CMSConcurrentMTEnabled"
>
> We are using cassandra 2.0.17. If anyone has any suggestion as to how what
> else we can look for to understand why this is happening please do reply.
>
>
>
> Thanks
> anishek
>
>
>

Re: Lot of GC on two nodes out of 7

[Jeff Jirsa]

Compaction falling behind will likely cause additional work on reads (more 
sstables to merge), but I’d be surprised if it manifested in super long GC. 
When you say twice as many sstables, how many is that?. 

In cfstats, does anything stand out? Is max row size on those nodes larger than 
on other nodes?

What you don’t show in your JVM options is the new gen size – if you do have 
unusually large partitions on those two nodes (especially likely if you have 
rf=2 – if you have rf=3, then there’s probably a third node misbehaving you 
haven’t found yet), then raising new gen size can help handle the garbage 
created by reading large partitions without having to tolerate the promotion. 
Estimates for the amount of garbage vary, but it could be “gigabytes” of 
garbage on a very wide partition (see 
https://issues.apache.org/jira/browse/CASSANDRA-9754 for work in progress to 
help mitigate that type of pain).

- Jeff 

From:  Anishek Agarwal
Reply-To:  "user@cassandra.apache.org"
Date:  Tuesday, March 1, 2016 at 11:12 PM
To:  "user@cassandra.apache.org"
Subject:  Lot of GC on two nodes out of 7

Hello, 

we have a cassandra cluster of 7 nodes, all of them have the same JVM GC 
configurations, all our writes /  reads use the TokenAware Policy wrapping a 
DCAware policy. All nodes are part of same Datacenter.

We are seeing that two nodes are having high GC collection times. Then mostly 
seem to spend time in GC like about 300-600 ms. This also seems to result in 
higher CPU utilisation on these machines. Other  5 nodes don't have this 
problem.

There is no additional repair activity going on the cluster, we are not sure 
why this is happening. 
we checked cfhistograms on the two CF we have in the cluster and number of 
reads seems to be almost same. 

we also used cfstats to see the number of ssttables on each node and one of the 
nodes with the above problem has twice the number of ssttables than other 
nodes. This still doesnot explain why two nodes have high GC Overheads. our GC 
config is as below:
JVM_OPTS="$JVM_OPTS -XX:+UseParNewGC"

JVM_OPTS="$JVM_OPTS -XX:+UseConcMarkSweepGC"

JVM_OPTS="$JVM_OPTS -XX:+CMSParallelRemarkEnabled"

JVM_OPTS="$JVM_OPTS -XX:SurvivorRatio=8"

JVM_OPTS="$JVM_OPTS -XX:MaxTenuringThreshold=50"

JVM_OPTS="$JVM_OPTS -XX:CMSInitiatingOccupancyFraction=70"

JVM_OPTS="$JVM_OPTS -XX:+UseCMSInitiatingOccupancyOnly"

JVM_OPTS="$JVM_OPTS -XX:+UseTLAB"

JVM_OPTS="$JVM_OPTS -XX:MaxPermSize=256m"

JVM_OPTS="$JVM_OPTS -XX:+AggressiveOpts"

JVM_OPTS="$JVM_OPTS -XX:+UseCompressedOops"

JVM_OPTS="$JVM_OPTS -XX:+CMSScavengeBeforeRemark"

JVM_OPTS="$JVM_OPTS -XX:ConcGCThreads=48"

JVM_OPTS="$JVM_OPTS -XX:ParallelGCThreads=48"

JVM_OPTS="$JVM_OPTS -XX:-ExplicitGCInvokesConcurrent"

JVM_OPTS="$JVM_OPTS -XX:+UnlockDiagnosticVMOptions"

JVM_OPTS="$JVM_OPTS -XX:+UseGCTaskAffinity"

JVM_OPTS="$JVM_OPTS -XX:+BindGCTaskThreadsToCPUs"

# earlier value 131072 = 32768 * 4

JVM_OPTS="$JVM_OPTS -XX:ParGCCardsPerStrideChunk=131072"

JVM_OPTS="$JVM_OPTS -XX:CMSScheduleRemarkEdenSizeThreshold=104857600"

JVM_OPTS="$JVM_OPTS -XX:CMSRescanMultiple=32768"

JVM_OPTS="$JVM_OPTS -XX:CMSConcMarkMultiple=32768"

#new 

JVM_OPTS="$JVM_OPTS -XX:+CMSConcurrentMTEnabled"


We are using cassandra 2.0.17. If anyone has any suggestion as to how what else 
we can look for to understand why this is happening please do reply. 



Thanks
anishek





smime.p7s
Description: S/MIME cryptographic signature

Lot of GC on two nodes out of 7

[Anishek Agarwal]

Hello,

we have a cassandra cluster of 7 nodes, all of them have the same JVM GC
configurations, all our writes /  reads use the TokenAware Policy wrapping
a DCAware policy. All nodes are part of same Datacenter.

We are seeing that two nodes are having high GC collection times. Then
mostly seem to spend time in GC like about 300-600 ms. This also seems to
result in higher CPU utilisation on these machines. Other  5 nodes don't
have this problem.

There is no additional repair activity going on the cluster, we are not
sure why this is happening.
we checked cfhistograms on the two CF we have in the cluster and number of
reads seems to be almost same.

we also used cfstats to see the number of ssttables on each node and one of
the nodes with the above problem has twice the number of ssttables than
other nodes. This still doesnot explain why two nodes have high GC
Overheads. our GC config is as below:

JVM_OPTS="$JVM_OPTS -XX:+UseParNewGC"

JVM_OPTS="$JVM_OPTS -XX:+UseConcMarkSweepGC"

JVM_OPTS="$JVM_OPTS -XX:+CMSParallelRemarkEnabled"

JVM_OPTS="$JVM_OPTS -XX:SurvivorRatio=8"

JVM_OPTS="$JVM_OPTS -XX:MaxTenuringThreshold=50"

JVM_OPTS="$JVM_OPTS -XX:CMSInitiatingOccupancyFraction=70"

JVM_OPTS="$JVM_OPTS -XX:+UseCMSInitiatingOccupancyOnly"

JVM_OPTS="$JVM_OPTS -XX:+UseTLAB"

JVM_OPTS="$JVM_OPTS -XX:MaxPermSize=256m"

JVM_OPTS="$JVM_OPTS -XX:+AggressiveOpts"

JVM_OPTS="$JVM_OPTS -XX:+UseCompressedOops"

JVM_OPTS="$JVM_OPTS -XX:+CMSScavengeBeforeRemark"

JVM_OPTS="$JVM_OPTS -XX:ConcGCThreads=48"

JVM_OPTS="$JVM_OPTS -XX:ParallelGCThreads=48"

JVM_OPTS="$JVM_OPTS -XX:-ExplicitGCInvokesConcurrent"

JVM_OPTS="$JVM_OPTS -XX:+UnlockDiagnosticVMOptions"

JVM_OPTS="$JVM_OPTS -XX:+UseGCTaskAffinity"

JVM_OPTS="$JVM_OPTS -XX:+BindGCTaskThreadsToCPUs"

# earlier value 131072 = 32768 * 4

JVM_OPTS="$JVM_OPTS -XX:ParGCCardsPerStrideChunk=131072"

JVM_OPTS="$JVM_OPTS -XX:CMSScheduleRemarkEdenSizeThreshold=104857600"

JVM_OPTS="$JVM_OPTS -XX:CMSRescanMultiple=32768"

JVM_OPTS="$JVM_OPTS -XX:CMSConcMarkMultiple=32768"

#new

JVM_OPTS="$JVM_OPTS -XX:+CMSConcurrentMTEnabled"

We are using cassandra 2.0.17. If anyone has any suggestion as to how what
else we can look for to understand why this is happening please do reply.



Thanks
anishek