ZooKeeper is a coordination service for distributed applications that ensures high throughput, low latency, and high availability without locks, providing features like leader election and configuration management. The document covers its architecture, installation procedures, various uses, stress test results, and concludes that increasing the number of servers enhances availability and performance while maintaining low latency. Key topics include service guarantees, client order, and reliable multicast capabilities.

1. ZooKeeper
Iuliia Proskurnia, Zygimantas Bruzgys

2. Outline
• ZooKeeper? • Experiments
• ZooKeeper Service • Configuration
• ZooKeeper Usage • Reliable Multicast
• Key Points
• Stress Test
• Installation
• Conclusions
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3. Key features
ZooKeeper is: Features are:
•Service for coordinating •High Throughput
processes in distributed
applications. •Low Latency
•Key/value table. •Highly Available
•No locks service. •Strictly ordered access to the
nodes
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4. Architecture
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5. ZooKeeper Service
• Znodes • Guarantees:
• Regular & Ephemeral • Linearizable writes
• Watches • FIFO client order
• Handling shared configuration
• Synchronous
and updates
Asynchronous methods
• Liveness and durability
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6. ZooKeeper Usage
• Simple Locks
• Configuration Management
• Simple Locks without Herd Effect
• Group membership
• Read/Write Locks
• Leader Election
• Double Barrier
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7. Key Points
• Wait-free protocol
• No Locks • But...
• Support Applications: • State Based System
• Configuration Management • Last changes visible
• Leader Election • Limited total size of data
• Group Membership
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8. Installation
To install you need to: Sample Configuration File:
•Install Java tickTime=2000
initLimit=10
•Download and extract syncLimit=5
clientPort=2181
ZooKeeper dataDir=/home/ubuntu/zoodata
•Write a configuration file server.1=10.227.206.23:2888:3888
•Write node ID in data server.2=10.58.190.233:2888:3888
server.3=10.234.121.38:2888:3888
directory (filename myid)
•Start ZooKeeper
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9. Experiments
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10. Configuration Management
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11. Reliable Multicast: Main
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12. Reliable Multicast: Leader Election
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13. Reliable Multicast:
Send Message
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14. Reliable Multicast: Receive Message
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15. Reliable Multicast:
Interesting Cases
• New client connects while a message is multicasted
• Recipient fails before receiving a message
• Leader fails
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16. Stress Tests
• Done with zk-latencies Python script
• Run with the following configuration
./zk-latencies.py --servers "CONNECTION_STRING" --znode_count=ZNODE_COUNT
--znode_size=100 --timeout=5000 --watch_multiple=2
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17. Stress Tests
14000"
Time#for#10.000#Async#Opera>ons#
12000"
10000"
8000"
Read" 1 client,
ms#
6000"
Write" multiple
4000" Watch"
servers
2000"
0"
1" 2" 3" 4" 5"
Number#of#Servers#in#ZooKeeper#Cluster#
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18. Stress Tests
7"
Synchronous+Opera)ons+
6"
5"
ms/opera)on+
4"
Read" 1 client,
3" Write" multiple
Watch"
2" servers
1"
0"
1" 2" 3" 4"
Number+of+Servers+in+ZooKeeper+Cluster+
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19. Stress Tests
1,2"
Writes+per+ms+
1"
ms/opera)on+
0,8"
0,6"
5 servers,
0,4" 1 client
0,2"
0"
1" 2" 4" 6" 8" 10" 12" 14" 16"
Thousands+of+Async+Opera)ons+
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20. Conclusions
• ZooKeeper is: • WeShowed Several
Examples:
• Coordination Service
• Configuration Management
• Highly Available
• Reliable Multicast
• Low Latency
• Wait-Free
• Stress Tests Shows:
• Prefer more servers for high availability and
higher reads/write ratio
• With more servers it is still low latency
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21. ZooKeeper
Iuliia Proskurnia, Zygimantas Bruzgys