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From Ran Tavory <ran...@gmail.com>
Subject Re: Overwhelming a cluster with writes?
Date Tue, 06 Apr 2010 06:46:37 GMT
Do you see one of the disks used by cassandra filled up when a node crashes?

On Tue, Apr 6, 2010 at 9:39 AM, Ilya Maykov <ivmaykov@gmail.com> wrote:

> I'm running the nodes with a JVM heap size of 6GB, and here are the
> related options from my storage-conf.xml. As mentioned in the first
> email, I left everything at the default value. I briefly googled
> around for "Cassandra performance tuning" etc but haven't found a
> definitive guide ... any help with tuning these parameters is greatly
> appreciated!
>
>  <DiskAccessMode>auto</DiskAccessMode>
>  <RowWarningThresholdInMB>512</RowWarningThresholdInMB>
>  <SlicedBufferSizeInKB>64</SlicedBufferSizeInKB>
>  <FlushDataBufferSizeInMB>32</FlushDataBufferSizeInMB>
>  <FlushIndexBufferSizeInMB>8</FlushIndexBufferSizeInMB>
>  <ColumnIndexSizeInKB>64</ColumnIndexSizeInKB>
>  <MemtableThroughputInMB>64</MemtableThroughputInMB>
>  <BinaryMemtableThroughputInMB>256</BinaryMemtableThroughputInMB>
>  <MemtableOperationsInMillions>0.3</MemtableOperationsInMillions>
>  <MemtableFlushAfterMinutes>60</MemtableFlushAfterMinutes>
>  <ConcurrentReads>8</ConcurrentReads>
>  <ConcurrentWrites>64</ConcurrentWrites>
>  <CommitLogSync>periodic</CommitLogSync>
>  <CommitLogSyncPeriodInMS>10000</CommitLogSyncPeriodInMS>
>  <GCGraceSeconds>864000</GCGraceSeconds>
>
> -- Ilya
>
> On Mon, Apr 5, 2010 at 11:26 PM, Boris Shulman <shulmanb@gmail.com> wrote:
> > You are running out of memory on your nodes. Before the final crash
> > your nodes are probably slow  due to GC. What is your memtable size?
> > What cache options did you configure?
> >
> > On Tue, Apr 6, 2010 at 7:31 AM, Ilya Maykov <ivmaykov@gmail.com> wrote:
> >> Hi all,
> >>
> >> I've just started experimenting with Cassandra to get a feel for the
> >> system. I've set up a test cluster and to get a ballpark idea of its
> >> performance I wrote a simple tool to load some toy data into the
> >> system. Surprisingly, I am able to "overwhelm" my 4-node cluster with
> >> writes from a single client. I'm trying to figure out if this is a
> >> problem with my setup, if I'm hitting bugs in the Cassandra codebase,
> >> or if this is intended behavior. Sorry this email is kind of long,
> >> here is the TLDR version:
> >>
> >> While writing to Cassandra from a single node, I am able to get the
> >> cluster into a bad state, where nodes are randomly disconnecting from
> >> each other, write performance plummets, and sometimes nodes even
> >> crash. Further, the nodes do not recover as long as the writes
> >> continue (even at a much lower rate), and sometimes do not recover at
> >> all unless I restart them. I can get this to happen simply by throwing
> >> data at the cluster fast enough, and I'm wondering if this is a known
> >> issue or if I need to tweak my setup.
> >>
> >> Now, the details.
> >>
> >> First, a little bit about the setup:
> >>
> >> 4-node cluster of identical machines, running cassandra-0.6.0-rc1 with
> >> the fixes for CASSANDRA-933, CASSANDRA-934, and CASSANDRA-936 patched
> >> in. Node specs:
> >> 8-core Intel Xeon E5405@2.00GHz
> >> 8GB RAM
> >> 1Gbit ethernet
> >> Red Hat Linux 2.6.18
> >> JVM 1.6.0_19 64-bit
> >> 1TB spinning disk houses both commitlog and data directories (which I
> >> know is not ideal).
> >> The client machine is on the same local network and has very similar
> specs.
> >>
> >> The cassandra nodes are started with the following JVM options:
> >>
> >> ./cassandra JVM_OPTS="-Xms6144m -Xmx6144m -XX:+UseConcMarkSweepGC -d64
> >> -XX:NewSize=1024m -XX:MaxNewSize=1024m -XX:+DisableExplicitGC"
> >>
> >> I'm using default settings for all of the tunable stuff at the bottom
> >> of storage-conf.xml. I also selected my initial tokens to evenly
> >> partition the key space when the cluster was bootstrapped. I am using
> >> the RandomPartitioner.
> >>
> >> Now, about the test. Basically I am trying to get an idea of just how
> >> fast I can make this thing go. I am writing ~250M data records into
> >> the cluster, replicated at 3x, using Ran Tavory's Hector client
> >> (Java), writing with ConsistencyLevel.ZERO and
> >> FailoverPolicy.FAIL_FAST. The client is using 32 threads with 8
> >> threads talking to each of the 4 nodes in the cluster. Records are
> >> identified by a numeric id, and I'm writing them in batches of up to
> >> 10k records per row, with each record in its own column. The row key
> >> identifies the bucket into which records fall. So, records with ids 0
> >> - 9999 are written to row "0", 10000 - 19999 are written to row
> >> "10000", etc. Each record is a JSON object with ~10-20 fields.
> >>
> >> Records: {  // Column Family
> >>   0 : {  // row key for the start of the bucket. Buckets span a range
> >> of up to 10000 records
> >>     1 : "{ /* some JSON */ }",  // Column for record with id=1
> >>     3 : "{ /* some more JSON */ }",  // Column for record with id=3
> >>    ...
> >>    9999 : "{ /* ... */ }"
> >>   },
> >>  10000 : {  // row key for the start of the next bucket
> >>    10001 : ...
> >>    10004 :
> >> }
> >>
> >> I am reading the data out of a local, sorted file on the client, so I
> >> only write a row to Cassandra once all records for that row have been
> >> read, and each row is written to exactly once. I'm using a
> >> producer-consumer queue to pump data from the input reader thread to
> >> the output writer threads. I found that I have to throttle the reader
> >> thread heavily in order to get good behavior. So, if I make the reader
> >> sleep for 7 seconds every 1M records, everything is fine - the data
> >> loads in about an hour, half of which is spent by the reader thread
> >> sleeping. In between the sleeps, I see ~40-50 MB/s throughput on the
> >> client's network interface while the reader is not sleeping, and it
> >> takes ~7-8 seconds to write each batch of 1M records.
> >>
> >> Now, if I remove the 7 second sleeps on the client side, things get
> >> bad after the first ~8M records are written to the client. Write
> >> throughput drops to <5 MB/s. I start seeing messages about nodes
> >> disconnecting and reconnecting in Cassandra's system.log, as well as
> >> lots of GC messages:
> >>
> >> ...
> >>  INFO [Timer-1] 2010-04-06 04:03:27,178 Gossiper.java (line 179)
> >> InetAddress /10.15.38.88 is now dead.
> >>  INFO [GC inspection] 2010-04-06 04:03:30,259 GCInspector.java (line
> >> 110) GC for ConcurrentMarkSweep: 2989 ms, 55326320 reclaimed leaving
> >> 1035998648 used; max is 1211170816
> >>  INFO [GC inspection] 2010-04-06 04:03:41,838 GCInspector.java (line
> >> 110) GC for ConcurrentMarkSweep: 3004 ms, 24377240 reclaimed leaving
> >> 1066120952 used; max is 1211170816
> >>  INFO [Timer-1] 2010-04-06 04:03:44,136 Gossiper.java (line 179)
> >> InetAddress /10.15.38.55 is now dead.
> >>  INFO [GMFD:1] 2010-04-06 04:03:44,138 Gossiper.java (line 568)
> >> InetAddress /10.15.38.55 is now UP
> >>  INFO [GC inspection] 2010-04-06 04:03:52,957 GCInspector.java (line
> >> 110) GC for ConcurrentMarkSweep: 2319 ms, 4504888 reclaimed leaving
> >> 1086023832 used; max is 1211170816
> >>  INFO [Timer-1] 2010-04-06 04:04:19,508 Gossiper.java (line 179)
> >> InetAddress /10.15.38.242 is now dead.
> >>  INFO [Timer-1] 2010-04-06 04:05:03,039 Gossiper.java (line 179)
> >> InetAddress /10.15.38.55 is now dead.
> >>  INFO [GMFD:1] 2010-04-06 04:05:03,041 Gossiper.java (line 568)
> >> InetAddress /10.15.38.55 is now UP
> >>  INFO [GC inspection] 2010-04-06 04:05:08,539 GCInspector.java (line
> >> 110) GC for ConcurrentMarkSweep: 2375 ms, 39534920 reclaimed leaving
> >> 1051620856 used; max is 1211170816
> >> ...
> >>
> >> Finally followed by this and some/all nodes going down:
> >>
> >> ERROR [COMPACTION-POOL:1] 2010-04-06 04:05:05,475
> >> DebuggableThreadPoolExecutor.java (line 94) Error in executor
> >> futuretask
> >> java.util.concurrent.ExecutionException: java.lang.OutOfMemoryError:
> >> Java heap space
> >>        at java.util.concurrent.FutureTask$Sync.innerGet(Unknown Source)
> >>        at java.util.concurrent.FutureTask.get(Unknown Source)
> >>        at
> org.apache.cassandra.concurrent.DebuggableThreadPoolExecutor.afterExecute(DebuggableThreadPoolExecutor.java:86)
> >>        at
> org.apache.cassandra.db.CompactionManager$CompactionExecutor.afterExecute(CompactionManager.java:582)
> >>        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)
> >> Caused by: java.lang.OutOfMemoryError: Java heap space
> >>        at java.util.Arrays.copyOf(Unknown Source)
> >>        at java.io.ByteArrayOutputStream.write(Unknown Source)
> >>        at java.io.DataOutputStream.write(Unknown Source)
> >>        at
> org.apache.cassandra.io.IteratingRow.echoData(IteratingRow.java:69)
> >>        at
> org.apache.cassandra.io.CompactionIterator.getReduced(CompactionIterator.java:138)
> >>        at
> org.apache.cassandra.io.CompactionIterator.getReduced(CompactionIterator.java:1)
> >>        at
> org.apache.cassandra.utils.ReducingIterator.computeNext(ReducingIterator.java:73)
> >>        at
> com.google.common.collect.AbstractIterator.tryToComputeNext(AbstractIterator.java:135)
> >>        at
> com.google.common.collect.AbstractIterator.hasNext(AbstractIterator.java:130)
> >>        at
> org.apache.commons.collections.iterators.FilterIterator.setNextObject(FilterIterator.java:183)
> >>        at
> org.apache.commons.collections.iterators.FilterIterator.hasNext(FilterIterator.java:94)
> >>        at
> org.apache.cassandra.db.CompactionManager.doCompaction(CompactionManager.java:299)
> >>        at
> org.apache.cassandra.db.CompactionManager$1.call(CompactionManager.java:102)
> >>        at
> org.apache.cassandra.db.CompactionManager$1.call(CompactionManager.java:1)
> >>        at java.util.concurrent.FutureTask$Sync.innerRun(Unknown Source)
> >>        at java.util.concurrent.FutureTask.run(Unknown Source)
> >>        ... 3 more
> >>
> >> At first I thought that with ConsistencyLevel.ZERO I must be doing
> >> async writes so Cassandra can't push back on the client threads (by
> >> blocking them), thus the server is getting overwhelmed. But, I would
> >> expect it to start dropping data and not crash in that case (after
> >> all, I did say ZERO so I can't expect any reliability, right?).
> >> However, I see similar slowdown / node dropout behavior when I set the
> >> consistency level to ONE. Does Cassandra push back on writers under
> >> heavy load? Is there some magic setting I need to tune to have it not
> >> fall over? Do I just need a bigger cluster? Thanks in advance,
> >>
> >> -- Ilya
> >>
> >> P.S. I realize that it's still handling a LOT of data with just 4
> >> nodes, and in practice nobody would run a system that gets 125k writes
> >> per second on top of a 4 node cluster. I was just surprised that I
> >> could make Cassandra fall over at all using a single client that's
> >> pumping data at 40-50 MB/s.
> >>
> >
>

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