data stax cassandra_summit_2013_cassandra_raspberrypi-rc1
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Hardware Agnostic: Cassandra on Raspberry Pi
Andy Cobley | Lecturer, University of Dundee, Scotland
* Cassandra is hardware agnostic* So why not run it on a Raspberry Pi ?* How hard can it be ?* What can we do with it once it works?
Cassandra on Raspberry Pi
* Andy Cobley* School of Computing* University of Dundee* Twitter: @andycobley
Who Am I ?
* Single chip Linux computer* 500 Meg ram* Boots off an SD card* Ethernet port * (graphics and all you need for a general purpose computer)
Whats a Raspberry Pi ?
Pi with pound coin
* And here’s the Cassandra cluster *
And, here’s one for real
* Power Permitting !
* Cassandra is designed to be fast, fast at writing, fast at reading.
* This laptop with one instance of Cassandra will do 12,000 write operations
* Raspberry Pi will do 200 !
The Bad News
* Running a external USB drive is actually worse !* Probably be hardware feature
More bad news !
Raspberry Pi Schematic
* Oracle Java vs OpenJDK
And then there’s Java!
* Raspbian is Debian for the PI* Uses the Hard floating point accelerator* Much faster than Debian* Current Oracle JDK won’t run on it !
And Raspbian
* http://www.oracle.com/technetwork/java/embedded/downloads/javase/index.html
* Java SE Embedded version 6* Cassandra might prefer 6* But* https://blogs.oracle.com/henrik/entry/
oracle_releases_jdk_for_linux* Preview at:* https://jdk8.java.net/fxarmpreview/
Oracle java
* Actually not much difference in performance
Hard vs Soft Float
* Cassandra uses compression for performance* Started in version 1.0
2x-4x reduction in data size25-35% performance improvement on reads5-10% performance improvement on writes
The Problem with compression
* Two types:
Google Snappy Compressor (Faster read/writes)DeflateCompressor (Java zip, slower , better compression)
* Snappy Compression not available on Pi
(requires native methods, so someone might get it to work!)
Compression types
* Startup script allocates memory* Calculates based on number of processors* Pi reports Zero processors !* Boom !* Now fixed
And the startup script
* In Cassandra-env.sh* JVM_OPTS="$JVM_OPTS -
Djava.rmi.server.hostname=192.168.1.15”* Or else nodetool will not work between nodes
JMX Config
* C* 1.22. added UseCondCardMark as a JVM Opt* "for better lock handling especially on hotspot with
multicore processor”* In cassandra-env.sh
#if [ "$JVM_VERSION" \> "1.7" ] ; then # JVM_OPTS="$JVM_OPTS -XX:+UseCondCardMark" #fi
JVM OPT UseCondCardMark
* We’ve forgotten one thing* The Pi cost £25* You can power 4 from USB hub (no need for a power
supply on each one)* So:
The Good News !
So, have a 64 node computer for £2000
University of Southhampton
* 32 node Beowolf cluster:* Joshua Kiepert, Boise University
Or this
* Adding nodes adds performance* Adding nodes adds replicas of data * BUT* Make sure your ring is balanced, * Pi’s don’t like to be unbalanced.
Adding nodes is good
* Vnodes (in 1.2) would be very nice* However at this point I haven’t got 1.2 on Pi running on a
cluster
Vnodes
Performance with 3/4 nodes
Performance with 5/6 nodes
* ./stress -d 192.168.1.10,192.168.1.11,192.168.1.12 -o insert -I DeflateCompressor
* Note: nodes to use* You will get different performance if you insert to less
nodes than you have in your ring
Stress test commands
* Adding a node (in the absence of Vnodes)
Must seed form a known nodeUse a program to calculate new keys Bring up new node with the correct key in cassandra.yamlUse node tool to move other nodes
Adding Nodes Procedure
* Python codeimport sysif (len(sys.argv) > 1): num = int(sys.argv[1])else: num = int(raw_input("How many nodes? :"))for i in range(0,num): print 'node %d: %d' % (i, (i*(2**127)/num))
Calculating keys
* Use nodetool
sudo ./nodetool -h 192.168.1.10 move 42535295865117307932921825928971026432
* And cleanup
./nodetool -h 192.168.1.10 cleanup
Moving existing nodes
* On Debian, you can free memory from the graphics chip
Cd /bootsudo cp start.elf start.elf.oldsudo cp arm224_start.elf to start.elfreboot
Getting more memory
* Under Rasbian* Run with a monitor plugged for the first time* Set options for screen memory* Perhaps disable boot to GUI
Getting more Memory
* I prefer static network addresses* Edit /etc/network/interfaces
iface eth0 inet static address 192.168.1.41 netmask 255.255.255.0 network 192.168.1.0 broadcast 192.168.1.255 gateway 192.168.1.254
*
Network address
* Make a master SD card* Copy it !* Make sure the master version has no data on it.* Consider ”Puppet” (though I don’t use it)
Multiple nodes
* See https://github.com/acobley/CassandraStartup * Put the file in /etc/init.d* update-rc.d cassandra defaults
Starting as a service
* So for £200 we get an 8 node C* cluster* It can be reconfigured, blown away, stress tested and
generally abused * We can simulate data racks, data centers and I hope even
long network delays.* Hopefully our upcoming MSc in Data Science will use these
clusters
Pi is for teaching
* We know C* can be configured to be aware of:
Network racksData Centers
* We know we can have replicas are stored across these racks
* How can we play with this cheaply ?
C* is network aware
Proposed teaching tool
10mbs Hubb
Noise injection
Switch 2
Switch 1
Pi 1
Pi 2
Pi 3
Pi 1
Pi 2
Pi 3
* Cassandra wouldn’t run on a PI* It does now.* Running it on a Pi shook out some Cassandra bugs* You can run it in a secure lab
Pi is discovery
* Most important, this was pure Geeky Fun
Pi is for fun
* Data Science:* http://www.computing.dundee.ac.uk/study/postgrad/degree
details.asp?17
Obligatory Plug
* Raspberry Pi is cheap* C* needs some work to run on it* You can make clusters cheaply for experimentation* It’s fun !
C* is Hardware Agnostic
THANK YOU