Re: Drop tables takes too long

[Alain RODRIGUEZ]

Hi

We were trying to overcome OOM crashes.


Fair enough :-).

We changed settings to default on one node. GC times became about two times
> smaller on that node.
>

That's encouraging! Looks like even if the number of tables is really high,
there is still space for optimization. Have you made the change on the
entire cluster by now? How are things going?

Also you can continue to play around with a canary node to find the sweet
spot, the right tuning for your use case and hardware. Taking a day to do
this is sometimes very worth it ;-).

Number of sstables is not constant. During about 2.5 hours number of tables
> was changed for 26 tables, e.g. [4, 4, 4, 4, 4, 4, 4, 4, 4, 4] => [6, 6,
> 6, 6, 6, 6, 6, 6, 6, 6] or [4, 7, 7, 7, 5, 5, 4, 4, 4, 4] => [4, 4, 4, 4,
> 4, 4, 4, 4, 4, 4] (each list is number of sstables on each of 10 nodes for
> one table).
> Number of sstables is balanced for almost all tables. But for some tables
> number of sstables is not really balanced, like [11, 2, 4, 4, 4, 2, 2, 2,
> 2, 5] or [439, 558, 346, 521, 490, 553, 500, 515, 522, 495]
>

Sounds like reasonable numbers of SSTables. Imbalances are not that big. I
would say compaction is running normally

 We run incremental repairs

 We use LCS for all tables and MVs. We don't do manual compactions (or
> trigger any anti-compactions)


If you run incremental repairs, it means you trigger anti-compactions.
Actually the first repair might completely have produce the increase in the
number of SSTables. If it was not the first time, you might have run into
one of the corner cases still not fixed on incremental repairs.

Also, using LCS for such a high number of tables is probably putting some
pressure on disks. Is it a real need? Would STCS or TWCS not be a better
fit on some of the table? That being said, compactions look good. Are you
seeing pending compactions under standard conditions or on peak hours?

 What number of MemtableFlushWriter are you using?
>
> We do not specify if, so default is use
>

https://github.com/apache/cassandra/blob/cassandra-3.10/conf/cassandra.yaml#L538

So it is 2. If disks IO is not a bottleneck you might want to consider
increasing this number to 4, it should be a safe value. To know if Flush
Writers is an issue, use 'watch -d nodetool tpstats' and see if there are
any 'FlushWriter' pending threads.

One column for each node
> READ:   2609 7   0   0   2   1   2   0   1   1
>

The only non negligible value is about read being dropped and on only one
node. If this value is not growing anymore, you might have faced a punctual
issue.

This cluster looks relatively healthy excepted for GC activity (that can
explain read drops). I would persevere on GC tuning, continuing to monitor
things you have been sharing with us so far, to see how it evolves. Having
a closer look at repairs impact might be worth it as well. Good luck!

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

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

2017-05-08 14:21 GMT+01:00 Bohdan Tantsiura :

> Hi,
>
> > Why did you move from defaults that much?
> We were trying to overcome OOM crashes.
>
> > Would you consider giving defaults a try on a canary node and monitor /
> compare GC times to other nodes?
> We changed settings to default on one node. GC times became about two
> times smaller on that node.
>
> > What do you mean from time to time? For how long are this task pending,
> what frequency is this happening?
>  CompactionExecutor pending tasks appeared on nodes once during 3 or more
> hours. Tasks were pending during about 5-15 minutes.
>
> > Is the number of sstables constant and balanced between nodes?
> Number of sstables is not constant. During about 2.5 hours number of
> tables was changed for 26 tables, e.g. [4, 4, 4, 4, 4, 4, 4, 4, 4, 4] =>
> [6, 6, 6, 6, 6, 6, 6, 6, 6, 6] or [4, 7, 7, 7, 5, 5, 4, 4, 4, 4] => [4,
> 4, 4, 4, 4, 4, 4, 4, 4, 4] (each list is number of sstables on each of 10
> nodes for one table).
> Number of sstables is balanced for almost all tables. But for some tables
> number of sstables is not really balanced, like [11, 2, 4, 4, 4, 2, 2, 2,
> 2, 5] or [439, 558, 346, 521, 490, 553, 500, 515, 522, 495]
>
> > Also do you run full or incremental repairs?
> We run incremental repairs
>
> > Do you use LCS or do some manual compactions (or trigger any
> anti-compactions)?
> We use LCS for all tables and MVs. We don't do manual compactions (or
> trigger any anti-compactions)
>
> > How is CPU doing, is there any burst in CPU that could be related to
> these errors?
> Unfortunately, stats for period when there were InternalResponseState
> pending tasks is lost.
>
> > What number of MemtableFlushWriter are you using
> We do not specify if, so default is used
>
> > What tasks were dropped
> One column for each node
> READ:   2609 7   0   0   2   1   2   0   1   1
> HINT:   00   0   0   

Re: Drop tables takes too long

[Bohdan Tantsiura]

Hi,

> Why did you move from defaults that much?
We were trying to overcome OOM crashes.

> Would you consider giving defaults a try on a canary node and monitor /
compare GC times to other nodes?
We changed settings to default on one node. GC times became about two times
smaller on that node.

> What do you mean from time to time? For how long are this task pending,
what frequency is this happening?
 CompactionExecutor pending tasks appeared on nodes once during 3 or more
hours. Tasks were pending during about 5-15 minutes.

> Is the number of sstables constant and balanced between nodes?
Number of sstables is not constant. During about 2.5 hours number of tables
was changed for 26 tables, e.g. [4, 4, 4, 4, 4, 4, 4, 4, 4, 4] => [6, 6, 6,
6, 6, 6, 6, 6, 6, 6] or [4, 7, 7, 7, 5, 5, 4, 4, 4, 4] => [4, 4, 4, 4, 4,
4, 4, 4, 4, 4] (each list is number of sstables on each of 10 nodes for one
table).
Number of sstables is balanced for almost all tables. But for some tables
number of sstables is not really balanced, like [11, 2, 4, 4, 4, 2, 2, 2,
2, 5] or [439, 558, 346, 521, 490, 553, 500, 515, 522, 495]

> Also do you run full or incremental repairs?
We run incremental repairs

> Do you use LCS or do some manual compactions (or trigger any
anti-compactions)?
We use LCS for all tables and MVs. We don't do manual compactions (or
trigger any anti-compactions)

> How is CPU doing, is there any burst in CPU that could be related to
these errors?
Unfortunately, stats for period when there were InternalResponseState
pending tasks is lost.

> What number of MemtableFlushWriter are you using
We do not specify if, so default is used

> What tasks were dropped
One column for each node
READ:   2609 7   0   0   2   1   2   0   1   1
HINT:   00   0   0   1   0   1   0   0   0
MUTATION:   00   1   0   0   0   0   0   0   0
REQUEST_RESPONSE:   00   0   0   2   0   0   0   0   1

Thanks

2017-05-03 17:00 GMT+03:00 Alain RODRIGUEZ :

> Hi,
>
> A few comments:
>
> Long GC Pauses take about one minute
>>
>
> This is huge. About JVM config, I haven't played much with G1GC, but the
> following seems to be a bad idea according to comments:
>
> ## Main G1GC tunable: lowering the pause target will lower throughput and
> vise versa.
> ## 200ms is the JVM default and lowest viable setting
> ## 1000ms increases throughput. Keep it smaller than the timeouts in
> cassandra.yaml.
> -XX:MaxGCPauseMillis=15000
>
> # Save CPU time on large (>= 16GB) heaps by delaying region scanning
> # until the heap is 70% full. The default in Hotspot 8u40 is 40%.
> -XX:InitiatingHeapOccupancyPercent=30
> # For systems with > 8 cores, the default ParallelGCThreads is 5/8 the
> number of logical cores.
> # Otherwise equal to the number of cores when 8 or less.
> # Machines with > 10 cores should try setting these to <= full cores.
> -XX:ParallelGCThreads=8
> # By default, ConcGCThreads is 1/4 of ParallelGCThreads.
> # Setting both to the same value can reduce STW durations.
> -XX:ConcGCThreads=8
>
>
> Why did you move from defaults that much? Would you consider
> giving defaults a try on a canary node and monitor / compare GC times to
> other nodes?
>
> 1) ColumnFamilyStore.java:542 - Failed unregistering mbean:
>> org.apache.cassandra.db:type=Tables,keyspace=...,table=...
>>  from MigrationStage thread
>>
>
> I am not sure about this one... :p
>
> 2) Read 1715 live rows and 1505 tombstone cells for query ...
>>  from ReadStage thread
>
>
> Half of what was read for this query was deleted data. With obvious disk
> space, disk throughput and latency consequences. This is an entire topic...
> Here is what I know about it: thelastpickle.com/blog/2016/07
> /27/about-deletes-and-tombstones.html, I hope it will help you solving
> your issue.
>
> 3) GCInspector.java:282 - G1 Young Generation GC in 1725ms
>
>
> This might be related to your GC configuration or some other issues
> mentioned in your last mail.
>
>  About 3000-6000 CompactionExecutor pending tasks appeared on all nodes
>> from time to time.
>
>
> Hum that's weird. It's huge, but as you have so many tables I am not sure,
> it might be a 'normal' issue when running with so many tables and MVs.
>
> What do you mean from time to time? For how long are this task pending,
> what frequency is this happening?
>
> Is the number of sstables constant and balanced between nodes?
> Also do you run full or incremental repairs?
> Do you use LCS or do some manual compactions (or trigger any
> anti-compactions)?
>
>
>> About 1000 MigrationStage pending tasks appeared on 2 nodes.
>
>
> That's pending writes. Meaning this Cassandra node can't cope with what
> what is thrown at it. It can be related to pending flushes (blocking
> writes), huge Garbage Collection (Stop The World, including writes), due to
> hardware limits (CPU busy with compactions?) or even to a too conservative
> configuration of the concurrent_write.
>
>
>> About 700 InternalResponseState 

Re: Drop tables takes too long

[Alain RODRIGUEZ]

Hi,

A few comments:

Long GC Pauses take about one minute
>

This is huge. About JVM config, I haven't played much with G1GC, but the
following seems to be a bad idea according to comments:

## Main G1GC tunable: lowering the pause target will lower throughput and
vise versa.
## 200ms is the JVM default and lowest viable setting
## 1000ms increases throughput. Keep it smaller than the timeouts in
cassandra.yaml.
-XX:MaxGCPauseMillis=15000

# Save CPU time on large (>= 16GB) heaps by delaying region scanning
# until the heap is 70% full. The default in Hotspot 8u40 is 40%.
-XX:InitiatingHeapOccupancyPercent=30
# For systems with > 8 cores, the default ParallelGCThreads is 5/8 the
number of logical cores.
# Otherwise equal to the number of cores when 8 or less.
# Machines with > 10 cores should try setting these to <= full cores.
-XX:ParallelGCThreads=8
# By default, ConcGCThreads is 1/4 of ParallelGCThreads.
# Setting both to the same value can reduce STW durations.
-XX:ConcGCThreads=8


Why did you move from defaults that much? Would you consider
giving defaults a try on a canary node and monitor / compare GC times to
other nodes?

1) ColumnFamilyStore.java:542 - Failed unregistering mbean:
> org.apache.cassandra.db:type=Tables,keyspace=...,table=...
>  from MigrationStage thread
>

I am not sure about this one... :p

2) Read 1715 live rows and 1505 tombstone cells for query ...
>  from ReadStage thread


Half of what was read for this query was deleted data. With obvious disk
space, disk throughput and latency consequences. This is an entire topic...
Here is what I know about it: thelastpickle.com/blog/2016/
07/27/about-deletes-and-tombstones.html, I hope it will help you solving
your issue.

3) GCInspector.java:282 - G1 Young Generation GC in 1725ms


This might be related to your GC configuration or some other issues
mentioned in your last mail.

 About 3000-6000 CompactionExecutor pending tasks appeared on all nodes
> from time to time.


Hum that's weird. It's huge, but as you have so many tables I am not sure,
it might be a 'normal' issue when running with so many tables and MVs.

What do you mean from time to time? For how long are this task pending,
what frequency is this happening?

Is the number of sstables constant and balanced between nodes?
Also do you run full or incremental repairs?
Do you use LCS or do some manual compactions (or trigger any
anti-compactions)?


> About 1000 MigrationStage pending tasks appeared on 2 nodes.


That's pending writes. Meaning this Cassandra node can't cope with what
what is thrown at it. It can be related to pending flushes (blocking
writes), huge Garbage Collection (Stop The World, including writes), due to
hardware limits (CPU busy with compactions?) or even to a too conservative
configuration of the concurrent_write.


> About 700 InternalResponseState pending tasks appeared on 2 nodes.


I never had issues with this one and so didn't knew much about it. But
according to Chris Lohfink in this post
https://www.pythian.com/blog/guide-to-cassandra-thread-pools/#InternalResponseStage,
this
thread pool is responsible for "Responding to non-client initiated
messages, including bootstrapping and schema checking". Which again might
be related with the huge number of tables in the cluster. How is CPU doing,
is there any burst in CPU that could be related to these errors?

About 60 MemtableFlushWriter appeared on 3 nodes.


What number of MemtableFlushWriter are you using. Consider increasing it
(or maybe the memtable size).


> There were no blocked tasks, but there were "All time blocked" tasks (they
> were before starting dropping tables) from 3 millions to 20 millions on
> different nodes.


What tasks were dropped.

The cluster doesn't look completely healthy, but I believe it is possible
to improve things, before thinking about splitting tables in multiples
cluster. I would definitely not add more tables though...

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

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

2017-04-28 14:35 GMT+01:00 Bohdan Tantsiura :

> Thanks Alain,
>
> > Or is it on happening during drop table actions?
> Some other schema changes (e.g. adding columns to tables) also takes too
> much time.
>
> Link to complete set of GC options: https://pastebin.com/4qyENeyu
>
> > Have you had a look at logs, mainly errors and warnings?
> In logs I found warnings of 3 types:
> 1) ColumnFamilyStore.java:542 - Failed unregistering mbean:
> org.apache.cassandra.db:type=Tables,keyspace=...,table=...
>  from MigrationStage thread
> 2) Read 1715 live rows and 1505 tombstone cells for query ...
>  from ReadStage thread
> 3) GCInspector.java:282 - G1 Young Generation GC in 1725ms.  G1 Eden
> Space: 38017171456 -> 0; G1 Survivor Space: 2516582400 <(251)%20658-2400>
> -> 2650800128; from Service Thread
>
> > Are they some pending, blocked or dropped tasks in thread pool 

Re: Drop tables takes too long

[Bohdan Tantsiura]

Thanks Alain,

> Or is it on happening during drop table actions?
Some other schema changes (e.g. adding columns to tables) also takes too
much time.

Link to complete set of GC options: https://pastebin.com/4qyENeyu

> Have you had a look at logs, mainly errors and warnings?
In logs I found warnings of 3 types:
1) ColumnFamilyStore.java:542 - Failed unregistering mbean:
org.apache.cassandra.db:type=Tables,keyspace=...,table=...
 from MigrationStage thread
2) Read 1715 live rows and 1505 tombstone cells for query ...
 from ReadStage thread
3) GCInspector.java:282 - G1 Young Generation GC in 1725ms.  G1 Eden Space:
38017171456 -> 0; G1 Survivor Space: 2516582400 -> 2650800128; from Service
Thread

> Are they some pending, blocked or dropped tasks in thread pool stats?
About 3000-6000 CompactionExecutor pending tasks appeared on all nodes from
time to time. About 1000 MigrationStage pending tasks appeared on 2 nodes.
About 700 InternalResponseState pending tasks appeared on 2 nodes. About
60 MemtableFlushWriter appeared on 3 nodes.
There were no blocked tasks, but there were "All time blocked" tasks (they
were before starting dropping tables) from 3 millions to 20 millions on
different nodes.

> Are some resources constraint (CPU / disk IO,...)?
CPU and disk IO are not constraint

Thanks

2017-04-27 11:10 GMT+03:00 Alain RODRIGUEZ :

> Hi
>
>
>> Long GC Pauses take about one minute. But why it takes so much time and
>> how that can be fixed?
>
>
> This is very long. Looks like you are having a major issue, and it is not
> just about dropping tables... Or is it on happening during drop table
> actions? Knowing the complete set of GC options in use could help here,
> could you paste it here (or link to it)?
>
> Also, GC is often high as a consequence of other issues and not only when
> 'badly‘ tuned
>
>
>- Have you had a look at logs, mainly errors and warnings?
>
>$ grep -e "ERROR" -e "WARN" /var/log/cassandra/system.log
>
>- Are they some pending, blocked or dropped tasks in thread pool
>stats?
>
>$ watch -d nodetool tpstats
>
>- Are some resources constraint (CPU / disk IO,...)?
>
>
> We have about 60 keyspaces with about 80 tables in each keyspace
>
> In each keyspace we also have 11 MVs
>
>
> Even if I believe we can dig it and maybe improve things, I agree with
> Carlos, this is a lot of Tables (4880) and even more a high number of MV
> (660). It might be interesting splitting it somehow if possible.
>
> Cannot achieve consistency level ALL
>
>
> Finally you could try to adjust the corresponding request timeout (not
> sure if it is the global one or the truncate timeout), so it may succeed
> even when nodes are having minutes GC, but it is a workaround as this
> minute GC will most definitely be an issue for the client queries running
> (default is 10 sec timeout, so many query are probably failing).
>
> C*heers,
> ---
> Alain Rodriguez - @arodream - al...@thelastpickle.com
> France
>
> The Last Pickle - Apache Cassandra Consulting
> http://www.thelastpickle.com
>
> 2017-04-25 13:58 GMT+02:00 Bohdan Tantsiura :
>
>> Thanks Zhao Yang,
>>
>> > Could you try some jvm tool to find out which thread are allocating
>> memory or gc? maybe the migration stage thread..
>>
>> I use Cassandra Cluster Manager to locally reproduce the issue. I tried
>> to use VisualVM to find out which threads are allocating memory, but VisualVM
>> does not see cassandra processes and says "Cannot open application with
>> pid". Then I tried to use YourKit Java Profiler. It created snapshot when
>> process of one cassandra node failed. http://i.imgur.com/9jBcjcl.png -
>> how CPU is used by threads. http://i.imgur.com/ox5Sozy.png - how memory
>> is used by threads, but biggest part of memory is used by objects without
>> allocation information. http://i.imgur.com/oqx9crX.png - which objects
>> use biggest part of memory. Maybe you know some other good jvm tool that
>> can show by which threads biggest part of memory is used?
>>
>> > BTW, is your cluster under high load while dropping table?
>>
>> LA5 was <= 5 on all nodes almost all time while dropping tables
>>
>> Thanks
>>
>> 2017-04-21 19:49 GMT+03:00 Jasonstack Zhao Yang <
>> zhaoyangsingap...@gmail.com>:
>>
>>> Hi Bohdan, Carlos,
>>>
>>> Could you try some jvm tool to find out which thread are allocating
>>> memory or gc? maybe the migration stage thread..
>>>
>>> BTW, is your cluster under high load while dropping table?
>>>
>>> As far as I remember, in older c* version, it applies the schema
>>> mutation in memory, ie. DROP, then flush all schema info into sstable, then
>>> reads all on disk schema into memory (5k tables info + related column
>>> info)..
>>>
>>> > You also might need to increase the node count if you're resource
>>> constrained.
>>>
>>> More nodes won't help and most probably make it worse due to
>>> coordination.
>>>
>>>
>>> Zhao Yang
>>>
>>>
>>>
>>> On Fri, 21 Apr 2017 at 

Re: Drop tables takes too long

[Alain RODRIGUEZ]

Hi


> Long GC Pauses take about one minute. But why it takes so much time and
> how that can be fixed?


This is very long. Looks like you are having a major issue, and it is not
just about dropping tables... Or is it on happening during drop table
actions? Knowing the complete set of GC options in use could help here,
could you paste it here (or link to it)?

Also, GC is often high as a consequence of other issues and not only when
'badly‘ tuned


   - Have you had a look at logs, mainly errors and warnings?

   $ grep -e "ERROR" -e "WARN" /var/log/cassandra/system.log

   - Are they some pending, blocked or dropped tasks in thread pool stats?

   $ watch -d nodetool tpstats

   - Are some resources constraint (CPU / disk IO,...)?


We have about 60 keyspaces with about 80 tables in each keyspace

In each keyspace we also have 11 MVs


Even if I believe we can dig it and maybe improve things, I agree with
Carlos, this is a lot of Tables (4880) and even more a high number of MV
(660). It might be interesting splitting it somehow if possible.

Cannot achieve consistency level ALL


Finally you could try to adjust the corresponding request timeout (not sure
if it is the global one or the truncate timeout), so it may succeed even
when nodes are having minutes GC, but it is a workaround as this minute GC
will most definitely be an issue for the client queries running (default is
10 sec timeout, so many query are probably failing).

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

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

2017-04-25 13:58 GMT+02:00 Bohdan Tantsiura :

> Thanks Zhao Yang,
>
> > Could you try some jvm tool to find out which thread are allocating
> memory or gc? maybe the migration stage thread..
>
> I use Cassandra Cluster Manager to locally reproduce the issue. I tried to
> use VisualVM to find out which threads are allocating memory, but VisualVM
> does not see cassandra processes and says "Cannot open application with
> pid". Then I tried to use YourKit Java Profiler. It created snapshot when
> process of one cassandra node failed. http://i.imgur.com/9jBcjcl.png -
> how CPU is used by threads. http://i.imgur.com/ox5Sozy.png - how memory
> is used by threads, but biggest part of memory is used by objects without
> allocation information. http://i.imgur.com/oqx9crX.png - which objects
> use biggest part of memory. Maybe you know some other good jvm tool that
> can show by which threads biggest part of memory is used?
>
> > BTW, is your cluster under high load while dropping table?
>
> LA5 was <= 5 on all nodes almost all time while dropping tables
>
> Thanks
>
> 2017-04-21 19:49 GMT+03:00 Jasonstack Zhao Yang <
> zhaoyangsingap...@gmail.com>:
>
>> Hi Bohdan, Carlos,
>>
>> Could you try some jvm tool to find out which thread are allocating
>> memory or gc? maybe the migration stage thread..
>>
>> BTW, is your cluster under high load while dropping table?
>>
>> As far as I remember, in older c* version, it applies the schema mutation
>> in memory, ie. DROP, then flush all schema info into sstable, then reads
>> all on disk schema into memory (5k tables info + related column info)..
>>
>> > You also might need to increase the node count if you're resource
>> constrained.
>>
>> More nodes won't help and most probably make it worse due to coordination.
>>
>>
>> Zhao Yang
>>
>>
>>
>> On Fri, 21 Apr 2017 at 21:10 Bohdan Tantsiura 
>> wrote:
>>
>>> Hi,
>>>
>>> Problem is still not solved. Does anybody have any idea what to do with
>>> it?
>>>
>>> Thanks
>>>
>>> 2017-04-20 15:05 GMT+03:00 Bohdan Tantsiura :
>>>
 Thanks Carlos,

 In each keyspace we also have 11 MVs.

 It is impossible to reduce number of tables now. Long GC Pauses take
 about one minute. But why it takes so much time and how that can be fixed?

 Each node in cluster has 128GB RAM, so resources are not constrained
 now

 Thanks

 2017-04-20 13:18 GMT+03:00 Carlos Rolo :

> You have 4800 Tables in total? That is a lot of tables, plus MVs? or
> MVs are already considered in the 60*80 account?
>
> I would recommend to reduce the table number. Other thing is that you
> need to check your log file for GC Pauses, and how long those pauses take.
>
> You also might need to increase the node count if you're resource
> constrained.
>
> Regards,
>
> Carlos Juzarte Rolo
> Cassandra Consultant / Datastax Certified Architect / Cassandra MVP
>
> Pythian - Love your data
>
> rolo@pythian | Twitter: @cjrolo | Skype: cjr2k3 | Linkedin:
> *linkedin.com/in/carlosjuzarterolo
> *
> Mobile: +351 918 918 100 <+351%20918%20918%20100>
> www.pythian.com
>
> On Thu, Apr 20, 2017 at 11:10 AM, Bohdan Tantsiura <
> 

Re: Drop tables takes too long

[Bohdan Tantsiura]

Thanks Zhao Yang,

> Could you try some jvm tool to find out which thread are allocating
memory or gc? maybe the migration stage thread..

I use Cassandra Cluster Manager to locally reproduce the issue. I tried to
use VisualVM to find out which threads are allocating memory, but VisualVM
does not see cassandra processes and says "Cannot open application with
pid". Then I tried to use YourKit Java Profiler. It created snapshot when
process of one cassandra node failed. http://i.imgur.com/9jBcjcl.png - how
CPU is used by threads. http://i.imgur.com/ox5Sozy.png - how memory is used
by threads, but biggest part of memory is used by objects without
allocation information. http://i.imgur.com/oqx9crX.png - which objects use
biggest part of memory. Maybe you know some other good jvm tool that can
show by which threads biggest part of memory is used?

> BTW, is your cluster under high load while dropping table?

LA5 was <= 5 on all nodes almost all time while dropping tables

Thanks

2017-04-21 19:49 GMT+03:00 Jasonstack Zhao Yang :

> Hi Bohdan, Carlos,
>
> Could you try some jvm tool to find out which thread are allocating memory
> or gc? maybe the migration stage thread..
>
> BTW, is your cluster under high load while dropping table?
>
> As far as I remember, in older c* version, it applies the schema mutation
> in memory, ie. DROP, then flush all schema info into sstable, then reads
> all on disk schema into memory (5k tables info + related column info)..
>
> > You also might need to increase the node count if you're resource
> constrained.
>
> More nodes won't help and most probably make it worse due to coordination.
>
>
> Zhao Yang
>
>
>
> On Fri, 21 Apr 2017 at 21:10 Bohdan Tantsiura  wrote:
>
>> Hi,
>>
>> Problem is still not solved. Does anybody have any idea what to do with
>> it?
>>
>> Thanks
>>
>> 2017-04-20 15:05 GMT+03:00 Bohdan Tantsiura :
>>
>>> Thanks Carlos,
>>>
>>> In each keyspace we also have 11 MVs.
>>>
>>> It is impossible to reduce number of tables now. Long GC Pauses take
>>> about one minute. But why it takes so much time and how that can be fixed?
>>>
>>> Each node in cluster has 128GB RAM, so resources are not constrained now
>>>
>>> Thanks
>>>
>>> 2017-04-20 13:18 GMT+03:00 Carlos Rolo :
>>>
 You have 4800 Tables in total? That is a lot of tables, plus MVs? or
 MVs are already considered in the 60*80 account?

 I would recommend to reduce the table number. Other thing is that you
 need to check your log file for GC Pauses, and how long those pauses take.

 You also might need to increase the node count if you're resource
 constrained.

 Regards,

 Carlos Juzarte Rolo
 Cassandra Consultant / Datastax Certified Architect / Cassandra MVP

 Pythian - Love your data

 rolo@pythian | Twitter: @cjrolo | Skype: cjr2k3 | Linkedin:
 *linkedin.com/in/carlosjuzarterolo
 *
 Mobile: +351 918 918 100 <+351%20918%20918%20100>
 www.pythian.com

 On Thu, Apr 20, 2017 at 11:10 AM, Bohdan Tantsiura  wrote:

> Hi,
>
> We are using cassandra 3.10 in a 10 nodes cluster with replication =
> 3. MAX_HEAP_SIZE=64GB on all nodes, G1 GC is used. We have about 60
> keyspaces with about 80 tables in each keyspace. We had to delete three
> tables and two materialized views from each keyspace. It began to take 
> more
> and more time for each next keyspace (for some keyspaces it took about 30
> minutes) and then failed with "Cannot achieve consistency level ALL". 
> After
> restarting the same repeated. It seems that cassandra hangs on GC. How 
> that
> can be solved?
>
> Thanks
>


 --




>>>
>>

Re: Drop tables takes too long

[Jasonstack Zhao Yang]

Hi Bohdan, Carlos,

Could you try some jvm tool to find out which thread are allocating memory
or gc? maybe the migration stage thread..

BTW, is your cluster under high load while dropping table?

As far as I remember, in older c* version, it applies the schema mutation
in memory, ie. DROP, then flush all schema info into sstable, then reads
all on disk schema into memory (5k tables info + related column info)..

> You also might need to increase the node count if you're resource
constrained.

More nodes won't help and most probably make it worse due to coordination.


Zhao Yang



On Fri, 21 Apr 2017 at 21:10 Bohdan Tantsiura  wrote:

> Hi,
>
> Problem is still not solved. Does anybody have any idea what to do with it?
>
> Thanks
>
> 2017-04-20 15:05 GMT+03:00 Bohdan Tantsiura :
>
>> Thanks Carlos,
>>
>> In each keyspace we also have 11 MVs.
>>
>> It is impossible to reduce number of tables now. Long GC Pauses take
>> about one minute. But why it takes so much time and how that can be fixed?
>>
>> Each node in cluster has 128GB RAM, so resources are not constrained now
>>
>> Thanks
>>
>> 2017-04-20 13:18 GMT+03:00 Carlos Rolo :
>>
>>> You have 4800 Tables in total? That is a lot of tables, plus MVs? or MVs
>>> are already considered in the 60*80 account?
>>>
>>> I would recommend to reduce the table number. Other thing is that you
>>> need to check your log file for GC Pauses, and how long those pauses take.
>>>
>>> You also might need to increase the node count if you're resource
>>> constrained.
>>>
>>> Regards,
>>>
>>> Carlos Juzarte Rolo
>>> Cassandra Consultant / Datastax Certified Architect / Cassandra MVP
>>>
>>> Pythian - Love your data
>>>
>>> rolo@pythian | Twitter: @cjrolo | Skype: cjr2k3 | Linkedin:
>>> *linkedin.com/in/carlosjuzarterolo
>>> *
>>> Mobile: +351 918 918 100 <+351%20918%20918%20100>
>>> www.pythian.com
>>>
>>> On Thu, Apr 20, 2017 at 11:10 AM, Bohdan Tantsiura 
>>> wrote:
>>>
 Hi,

 We are using cassandra 3.10 in a 10 nodes cluster with replication = 3.
 MAX_HEAP_SIZE=64GB on all nodes, G1 GC is used. We have about 60 keyspaces
 with about 80 tables in each keyspace. We had to delete three tables and
 two materialized views from each keyspace. It began to take more and more
 time for each next keyspace (for some keyspaces it took about 30 minutes)
 and then failed with "Cannot achieve consistency level ALL". After
 restarting the same repeated. It seems that cassandra hangs on GC. How that
 can be solved?

 Thanks

>>>
>>>
>>> --
>>>
>>>
>>>
>>>
>>
>

Re: Drop tables takes too long

[Bohdan Tantsiura]

Hi,

Problem is still not solved. Does anybody have any idea what to do with it?

Thanks

2017-04-20 15:05 GMT+03:00 Bohdan Tantsiura :

> Thanks Carlos,
>
> In each keyspace we also have 11 MVs.
>
> It is impossible to reduce number of tables now. Long GC Pauses take about
> one minute. But why it takes so much time and how that can be fixed?
>
> Each node in cluster has 128GB RAM, so resources are not constrained now
>
> Thanks
>
> 2017-04-20 13:18 GMT+03:00 Carlos Rolo :
>
>> You have 4800 Tables in total? That is a lot of tables, plus MVs? or MVs
>> are already considered in the 60*80 account?
>>
>> I would recommend to reduce the table number. Other thing is that you
>> need to check your log file for GC Pauses, and how long those pauses take.
>>
>> You also might need to increase the node count if you're resource
>> constrained.
>>
>> Regards,
>>
>> Carlos Juzarte Rolo
>> Cassandra Consultant / Datastax Certified Architect / Cassandra MVP
>>
>> Pythian - Love your data
>>
>> rolo@pythian | Twitter: @cjrolo | Skype: cjr2k3 | Linkedin:
>> *linkedin.com/in/carlosjuzarterolo
>> *
>> Mobile: +351 918 918 100 <+351%20918%20918%20100>
>> www.pythian.com
>>
>> On Thu, Apr 20, 2017 at 11:10 AM, Bohdan Tantsiura 
>> wrote:
>>
>>> Hi,
>>>
>>> We are using cassandra 3.10 in a 10 nodes cluster with replication = 3.
>>> MAX_HEAP_SIZE=64GB on all nodes, G1 GC is used. We have about 60 keyspaces
>>> with about 80 tables in each keyspace. We had to delete three tables and
>>> two materialized views from each keyspace. It began to take more and more
>>> time for each next keyspace (for some keyspaces it took about 30 minutes)
>>> and then failed with "Cannot achieve consistency level ALL". After
>>> restarting the same repeated. It seems that cassandra hangs on GC. How that
>>> can be solved?
>>>
>>> Thanks
>>>
>>
>>
>> --
>>
>>
>>
>>
>

Re: Drop tables takes too long

[Bohdan Tantsiura]

Thanks Carlos,

In each keyspace we also have 11 MVs.

It is impossible to reduce number of tables now. Long GC Pauses take about
one minute. But why it takes so much time and how that can be fixed?

Each node in cluster has 128GB RAM, so resources are not constrained now

Thanks

2017-04-20 13:18 GMT+03:00 Carlos Rolo :

> You have 4800 Tables in total? That is a lot of tables, plus MVs? or MVs
> are already considered in the 60*80 account?
>
> I would recommend to reduce the table number. Other thing is that you need
> to check your log file for GC Pauses, and how long those pauses take.
>
> You also might need to increase the node count if you're resource
> constrained.
>
> Regards,
>
> Carlos Juzarte Rolo
> Cassandra Consultant / Datastax Certified Architect / Cassandra MVP
>
> Pythian - Love your data
>
> rolo@pythian | Twitter: @cjrolo | Skype: cjr2k3 | Linkedin:
> *linkedin.com/in/carlosjuzarterolo
> *
> Mobile: +351 918 918 100 <+351%20918%20918%20100>
> www.pythian.com
>
> On Thu, Apr 20, 2017 at 11:10 AM, Bohdan Tantsiura 
> wrote:
>
>> Hi,
>>
>> We are using cassandra 3.10 in a 10 nodes cluster with replication = 3.
>> MAX_HEAP_SIZE=64GB on all nodes, G1 GC is used. We have about 60 keyspaces
>> with about 80 tables in each keyspace. We had to delete three tables and
>> two materialized views from each keyspace. It began to take more and more
>> time for each next keyspace (for some keyspaces it took about 30 minutes)
>> and then failed with "Cannot achieve consistency level ALL". After
>> restarting the same repeated. It seems that cassandra hangs on GC. How that
>> can be solved?
>>
>> Thanks
>>
>
>
> --
>
>
>
>

Re: Drop tables takes too long

[Carlos Rolo]

You have 4800 Tables in total? That is a lot of tables, plus MVs? or MVs
are already considered in the 60*80 account?

I would recommend to reduce the table number. Other thing is that you need
to check your log file for GC Pauses, and how long those pauses take.

You also might need to increase the node count if you're resource
constrained.

Regards,

Carlos Juzarte Rolo
Cassandra Consultant / Datastax Certified Architect / Cassandra MVP

Pythian - Love your data

rolo@pythian | Twitter: @cjrolo | Skype: cjr2k3 | Linkedin:
*linkedin.com/in/carlosjuzarterolo
*
Mobile: +351 918 918 100
www.pythian.com

On Thu, Apr 20, 2017 at 11:10 AM, Bohdan Tantsiura 
wrote:

> Hi,
>
> We are using cassandra 3.10 in a 10 nodes cluster with replication = 3.
> MAX_HEAP_SIZE=64GB on all nodes, G1 GC is used. We have about 60 keyspaces
> with about 80 tables in each keyspace. We had to delete three tables and
> two materialized views from each keyspace. It began to take more and more
> time for each next keyspace (for some keyspaces it took about 30 minutes)
> and then failed with "Cannot achieve consistency level ALL". After
> restarting the same repeated. It seems that cassandra hangs on GC. How that
> can be solved?
>
> Thanks
>

-- 


--

Drop tables takes too long

[Bohdan Tantsiura]

Hi,

We are using cassandra 3.10 in a 10 nodes cluster with replication = 3.
MAX_HEAP_SIZE=64GB on all nodes, G1 GC is used. We have about 60 keyspaces
with about 80 tables in each keyspace. We had to delete three tables and
two materialized views from each keyspace. It began to take more and more
time for each next keyspace (for some keyspaces it took about 30 minutes)
and then failed with "Cannot achieve consistency level ALL". After
restarting the same repeated. It seems that cassandra hangs on GC. How that
can be solved?

Thanks