Some updates:
Since we still have not fully turned on the system. We did something crazy
today. We tried to treat the node as dead one. (My boss wants us to practice
replacing a dead node before going to full production) and boot strap it. Here
is what we did:
* drain the node
* check nodetool on other nodes, and this node is marked down (the token
for this node is 100)
* clear the data, commit log, saved cache
* change initial_token from 100 to 99 in the yaml file
* start the node
* check nodetool, the down node of 100 disappeared by itself (!!) and new
node with token 99 showed up
* checked log, see the message saying bootstrap completed. But only a
couple of MB streamed.
* nodetool movetoken 98
* nodetool, see the node with token 98 comes up.
* check log, s ee the message saying bootstrap completed. But still only a
couple of MB streamed.
The only reason I can think of is that the new node has the same IP as the
"dead" node we tried to replace? Will that cause the symptom of no data
streamed from other nodes? Other nodes still think the node had all the data?
We had to do nodetool repair -pr to bring in the data. After 3 hours, 150G
transferred. And no surprise, pending compaction tasks are now at 30K. There
are about 30K SStable transferred and I guess all of them needs to be compacted
since we use LCS.
My concern is that if we did nothing wrong, replacing a dead node will cause
such a hugh back log of pending compaction. It might take a week to clear that
off. And we have RF = 3, we still need to bring in the data for the other two
replicates since we use "pr" for nodetool repair. It will take about 3 weeks to
fully replace a 200G node using LCS? We tried everything we can to speed up the
compaction and no luck. The only thing I can think of is to increase the
default size of SSTable, so less number of compaction will be needed. Can I
just change it in yaml and restart C* and it will correct itself? Any side
effect? Since we are using SSD, a bit bigger SSD won't slow down the read too
much, I suppose that is the main concern for bigger size of SSTable?
I think 1.2 comes with parallel LC which should help the situation. But we are
not going to upgrade for a little while.
Did I miss anything? It might not be practical to use LCS for 200G node? But if
we use Sized compaction, we need to have at least 400G for the HD...Although
SSD is cheap now, still hard to convince the management. three replicates +
double the Disk for compaction? that is 6 times of the real data size!
Sorry for the long email. Any suggestion or advice?
Thanks.
-Wei
----- Original Message -----
From: "aaron morton" <aa...@thelastpickle.com>
To: "Cassandra User" <user@cassandra.apache.org>
Sent: Tuesday, January 29, 2013 12:59:42 PM
Subject: Re: Cassandra pending compaction tasks keeps increasing
* Will try it tomorrow. Do I need to restart server to change the log level?
You can set it via JMX, and supposedly log4j is configured to watch the config
file.
Cheers
-----------------
Aaron Morton
Freelance Cassandra Developer
New Zealand
@aaronmorton
http://www.thelastpickle.com
On 29/01/2013, at 9:36 PM, Wei Zhu < wz1...@yahoo.com > wrote:
<blockquote>
Thanks for the reply. Here is some information:
Do you have wide rows ? Are you seeing logging about "Compacting wide rows" ?
* I don't see any log about "wide rows"
Are you seeing GC activity logged or seeing CPU steal on a VM ?
* There is some GC, but CPU general is under 20%. We have heap size of 8G, RAM
is at 72G.
Have you tried disabling multithreaded_compaction ?
* By default, it's disabled. We enabled it, but doesn't see much difference.
Even a little slower with it's enabled. Is it bad to enable it? We have SSD,
according to comment in yaml, it should help while using SSD.
Are you using Key Caches ? Have you tried disabling
compaction_preheat_key_cache?
* We have fairly big Key caches, we set as 10% of Heap which is 800M. Yes,
compaction_preheat_key_cache is disabled.
Can you enabled DEBUG level logging and make them available ?
* Will try it tomorrow. Do I need to restart server to change the log level?
-Wei
----- Original Message -----
From: "aaron morton" < aa...@thelastpickle.com >
To: user@cassandra.apache.org
Sent: Monday, January 28, 2013 11:31:42 PM
Subject: Re: Cassandra pending compaction tasks keeps increasing
* Why nodetool repair increases the data size that much? It's not likely that
much data needs to be repaired. Will that happen for all the subsequent repair?
Repair only detects differences in entire rows. If you have very wide rows then
small differences in rows can result in a large amount of streaming.
Streaming creates new SSTables on the receiving side, which then need to be
compacted. So repair often results in compaction doing it's thing for a while.
* How to make LCS run faster? After almost a day, the LCS tasks only dropped by
1000. I am afraid it will never catch up. We set
This is going to be tricky to diagnose, sorry for asking silly questions...
Do you have wide rows ? Are you seeing logging about "Compacting wide rows" ?
Are you seeing GC activity logged or seeing CPU steal on a VM ?
Have you tried disabling multithreaded_compaction ?
Are you using Key Caches ? Have you tried disabling
compaction_preheat_key_cache?
Can you enabled DEBUG level logging and make them available ?
Cheers
-----------------
Aaron Morton
Freelance Cassandra Developer
New Zealand
@aaronmorton
http://www.thelastpickle.com
On 29/01/2013, at 8:59 AM, Derek Williams < de...@fyrie.net > wrote:
I could be wrong about this, but when repair is run, it isn't just values that
are streamed between nodes, it's entire sstables. This causes a lot of
duplicate data to be written which was already correct on the node, which needs
to be compacted away.
As for speeding it up, no idea.
On Mon, Jan 28, 2013 at 12:16 PM, Wei Zhu < wz1...@yahoo.com > wrote:
Any thoughts?
Thanks.
-Wei
----- Original Message -----
From: "Wei Zhu" < wz1...@yahoo.com >
To: user@cassandra.apache.org
Sent: Friday, January 25, 2013 10:09:37 PM
Subject: Re: Cassandra pending compaction tasks keeps increasing
To recap the problem,
1.1.6 on SSD, 5 nodes, RF = 3, one CF only.
After data load, initially all 5 nodes have very even data size (135G, each). I
ran nodetool repair -pr on node 1 which have replicates on node 2, node 3 since
we set RF = 3.
It appears that huge amount of data got transferred. Node 1 has 220G, node 2, 3
have around 170G. Pending LCS task on node 1 is 15K and node 2, 3 have around
7K each.
Questions:
* Why nodetool repair increases the data size that much? It's not likely that
much data needs to be repaired. Will that happen for all the subsequent repair?
* How to make LCS run faster? After almost a day, the LCS tasks only dropped by
1000. I am afraid it will never catch up. We set
* compaction_throughput_mb_per_sec = 500
* multithreaded_compaction: true
Both Disk and CPU util are less than 10%. I understand LCS is single threaded,
any chance to speed it up?
* We use default SSTable size as 5M, Will increase the size of SSTable help?
What will happen if I change the setting after the data is loaded.
Any suggestion is very much appreciated.
-Wei
----- Original Message -----
From: "Wei Zhu" < wz1...@yahoo.com >
To: user@cassandra.apache.org
Sent: Thursday, January 24, 2013 11:46:04 PM
Subject: Re: Cassandra pending compaction tasks keeps increasing
I believe I am running into this one:
https://issues.apache.org/jira/browse/CASSANDRA-4765
By the way, I am using 1.1.6 (I though I was using 1.1.7) and this one is fixed
in 1.1.7.
----- Original Message -----
From: "Wei Zhu" < wz1...@yahoo.com >
To: user@cassandra.apache.org
Sent: Thursday, January 24, 2013 11:18:59 PM
Subject: Re: Cassandra pending compaction tasks keeps increasing
Thanks Derek,
in the cassandra-env.sh, it says
# reduce the per-thread stack size to minimize the impact of Thrift
# thread-per-client. (Best practice is for client connections to
# be pooled anyway.) Only do so on Linux where it is known to be
# supported.
# u34 and greater need 180k
JVM_OPTS="$JVM_OPTS -Xss180k"
What value should I use? Java defaults at 400K? Maybe try that first.
Thanks.
-Wei
----- Original Message -----
From: "Derek Williams" < de...@fyrie.net >
To: user@cassandra.apache.org , "Wei Zhu" < wz1...@yahoo.com >
Sent: Thursday, January 24, 2013 11:06:00 PM
Subject: Re: Cassandra pending compaction tasks keeps increasing
Increasing the stack size in cassandra-env.sh should help you get past the
stack overflow. Doesn't help with your original problem though.
On Fri, Jan 25, 2013 at 12:00 AM, Wei Zhu < wz1...@yahoo.com > wrote:
Well, even after restart, it throws the the same exception. I am basically
stuck. Any suggestion to clear the pending compaction tasks? Below is the end
of stack trace:
at com.google.common.collect.Sets$1.iterator(Sets.java:578)
at com.google.common.collect.Sets$1.iterator(Sets.java:578)
at com.google.common.collect.Sets$1.iterator(Sets.java:578)
at com.google.common.collect.Sets$1.iterator(Sets.java:578)
at com.google.common.collect.Sets$3.iterator(Sets.java:667)
at com.google.common.collect.Sets$3.size(Sets.java:670)
at com.google.common.collect.Iterables.size(Iterables.java:80)
at org.apache.cassandra.db.DataTracker.buildIntervalTree(DataTracker.java:557)
at
org.apache.cassandra.db.compaction.CompactionController.<init>(CompactionController.java:69)
at
org.apache.cassandra.db.compaction.CompactionTask.execute(CompactionTask.java:105)
at
org.apache.cassandra.db.compaction.LeveledCompactionTask.execute(LeveledCompactionTask.java:50)
at
org.apache.cassandra.db.compaction.CompactionManager$1.runMayThrow(CompactionManager.java:154)
at org.apache.cassandra.utils.WrappedRunnable.run(WrappedRunnable.java:30)
at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
at java.util.concurrent.FutureTask$Sync.innerRun(Unknown Source)
at java.util.concurrent.FutureTask.run(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
Any suggestion is very much appreciated
-Wei
----- Original Message -----
From: "Wei Zhu" < wz1...@yahoo.com >
To: user@cassandra.apache.org
Sent: Thursday, January 24, 2013 10:55:07 PM
Subject: Re: Cassandra pending compaction tasks keeps increasing
Do you mean 90% of the reads should come from 1 SSTable?
By the way, after I finished the data migrating, I ran nodetool repair -pr on
one of the nodes. Before nodetool repair, all the nodes have the same disk
space usage. After I ran the nodetool repair, the disk space for that node
jumped from 135G to 220G, also there are more than 15000 pending compaction
tasks. After a while , Cassandra started to throw the exception like below and
stop compacting. I had to restart the node. By the way, we are using 1.1.7.
Something doesn't seem right.
INFO [CompactionExecutor:108804] 2013-01-24 22:23:10,427 CompactionTask.java
(line 109) Compacting
[SSTableReader(path='/ssd/cassandra/data/zoosk/friends/zoosk-friends-hf-753782-Data.db')]
INFO [CompactionExecutor:108804] 2013-01-24 22:23:11,610 CompactionTask.java
(line 221) Compacted to
[/ssd/cassandra/data/zoosk/friends/zoosk-friends-hf-754996-Data.db,]. 5,259,403
to 5,259,403 (~100% of original) bytes for 1,983 keys at 4.268730MB/s. Time:
1,175ms.
INFO [CompactionExecutor:108805] 2013-01-24 22:23:11,617 CompactionTask.java
(line 109) Compacting
[SSTableReader(path='/ssd/cassandra/data/zoosk/friends/zoosk-friends-hf-754880-Data.db')]
INFO [CompactionExecutor:108805] 2013-01-24 22:23:12,828 CompactionTask.java
(line 221) Compacted to
[/ssd/cassandra/data/zoosk/friends/zoosk-friends-hf-754997-Data.db,]. 5,272,746
to 5,272,746 (~100% of original) bytes for 1,941 keys at 4.152339MB/s. Time:
1,211ms.
ERROR [CompactionExecutor:108806] 2013-01-24 22:23:13,048
AbstractCassandraDaemon.java (line 135) Exception in thread
Thread[CompactionExecutor:108806,1,main]
java.lang.StackOverflowError
at java.util.AbstractList$Itr.hasNext(Unknown Source)
at com.google.common.collect.Iterators$5.hasNext(Iterators.java:517)
at com.google.common.collect.Iterators$3.hasNext(Iterators.java:114)
at com.google.common.collect.Iterators$5.hasNext(Iterators.java:517)
at com.google.common.collect.Iterators$3.hasNext(Iterators.java:114)
at com.google.common.collect.Iterators$5.hasNext(Iterators.java:517)
at com.google.common.collect.Iterators$3.hasNext(Iterators.java:114)
at com.google.common.collect.Iterators$5.hasNext(Iterators.java:517)
at com.google.common.collect.Iterators$3.hasNext(Iterators.java:114)
----- Original Message -----
From: "aaron morton" < aa...@thelastpickle.com >
To: user@cassandra.apache.org
Sent: Wednesday, January 23, 2013 2:40:45 PM
Subject: Re: Cassandra pending compaction tasks keeps increasing
The histogram does not look right to me, too many SSTables for an LCS CF.
It's a symptom no a cause. If LCS is catching up though it should be more like
the distribution in the linked article.
Cheers
-----------------
Aaron Morton
Freelance Cassandra Developer
New Zealand
@aaronmorton
http://www.thelastpickle.com
On 23/01/2013, at 10:57 AM, Jim Cistaro < jcist...@netflix.com > wrote:
What version are you using? Are you seeing any compaction related assertions in
the logs?
Might be https://issues.apache.org/jira/browse/CASSANDRA-4411
We experienced this problem of the count only decreasing to a certain number
and then stopping. If you are idle, it should go to 0. I have not seen it
overestimate for zero, only for non-zero amounts.
As for timeouts etc, you will need to look at things like nodetool tpstats to
see if you have pending transactions queueing up.
Jc
From: Wei Zhu < wz1...@yahoo.com >
Reply-To: " user@cassandra.apache.org " < user@cassandra.apache.org >, Wei Zhu
< wz1...@yahoo.com >
Date: Tuesday, January 22, 2013 12:56 PM
To: " user@cassandra.apache.org " < user@cassandra.apache.org >
Subject: Re: Cassandra pending compaction tasks keeps increasing
Thanks Aaron and Jim for your reply. The data import is done. We have about
135G on each node and it's about 28K SStables. For normal operation, we only
have about 90 writes per seconds, but when I ran nodetool compationstats, it
remains at 9 and hardly changes. I guess it's just an estimated number.
When I ran histogram,
Offset SSTables Write Latency Read Latency Row Size Column Count
1 2644 0 0 0 18660057
2 8204 0 0 0 9824270
3 11198 0 0 0 6968475
4 4269 6 0 0 5510745
5 517 29 0 0 4595205
You can see about half of the reads result in 3 SSTables. Majority of read
latency are under 5ms, only a dozen are over 10ms. We haven't fully turn on
reads yet, only 60 reads per second. We see about 20 read timeout during the
past 12 hours. Not a single warning from Cassandra Log.
Is it normal for Cassandra to timeout some requests? We set rpc timeout to be
1s, it shouldn't time out any of them?
Thanks.
-Wei
From: aaron morton < aa...@thelastpickle.com >
To: user@cassandra.apache.org
Sent: Monday, January 21, 2013 12:21 AM
Subject: Re: Cassandra pending compaction tasks keeps increasing
The main guarantee LCS gives you is that most reads will only touch 1 row
http://www.datastax.com/dev/blog/when-to-use-leveled-compaction
If compaction is falling behind this may not hold.
nodetool cfhistograms tells you how many SSTables were read from for reads.
It's a recent histogram that resets each time you read from it.
Also, parallel levelled compaction in 1.2
http://www.datastax.com/dev/blog/performance-improvements-in-cassandra-1-2
Cheers
-----------------
Aaron Morton
Freelance Cassandra Developer
New Zealand
@aaronmorton
http://www.thelastpickle.com
On 20/01/2013, at 7:49 AM, Jim Cistaro < jcist...@netflix.com > wrote:
1) In addition to iostat, dstat is a good tool to see wht kind of disck
throuput your are getting. That would be one thing to monitor.
2) For LCS, we also see pending compactions skyrocket. During load, LCS will
create a lot of small sstables which will queue up for compaction.
3) For us the biggest concern is not how high the pending count gets, but how
often it gets back down near zero. If your load is something you can do in
segments or pause, then you can see how fast the cluster recovers on the
compactions.
4) One thing which we tune per cluster is the size of the files. Increasing
this from 5MB can sometimes improve things. But I forget if we have ever
changed this after starting data load.
Is your cluster receiving read traffic during this data migration? If so, I
would say that read latency is your best measure. If the high number of
SSTables waiting to compact is not hurting your reads, then you are probably
ok. Since you are on SSD, there is a good chance the compactions are not
hurting you. As for compactionthroughput, we set ours high for SSD. You usually
wont use it all because the compactions are usually single threaded. Dstat will
help you measure this.
I hope this helps,
jc
From: Wei Zhu < wz1...@yahoo.com >
Reply-To: " user@cassandra.apache.org " < user@cassandra.apache.org >, Wei Zhu
< wz1...@yahoo.com >
Date: Friday, January 18, 2013 12:10 PM
To: Cassandr usergroup < user@cassandra.apache.org >
Subject: Cassandra pending compaction tasks keeps increasing
Hi,
When I run nodetool compactionstats
I see the number of pending tasks keep going up steadily.
I tried to increase the compactionthroughput, by using
nodetool setcompactionthroughput
I even tried the extreme to set it to 0 to disable the throttling.
I checked iostats and we have SSD for data, the disk util is less than 5% which
means it's not I/O bound, CPU is also less than 10%
We are using levelcompaction and in the process of migrating data. We have 4500
writes per second and very few reads. We have about 70G data now and will grow
to 150G when the migration finishes. We only have one CF and right now the
number of SSTable is around 15000, write latency is still under 0.1ms.
Anything needs to be concerned? Or anything I can do to reduce the number of
pending compaction?
Thanks.
-Wei
--
Derek Williams
--
Derek Williams
</blockquote>
