1. Dynamic Slot Allocation Technique for MapReduce Clusters School of Computer Engineering Nanyang Technological University 25 th Sept 2013 Shanjiang Tang, Bu-Sung Lee, Bingsheng He 1

2. OutLine Background & Motivations DHFS Evaluation Conclusion 2

3. MapReduce Computation Model Map Intermediate Result Map Reduce Output Result Reduce Output Result Reduce Output Result Reduce Output Result Final Result Map-Phase Computation Reduce-Phase Computation Input Data 3

4. Hadoop Execution Model Hadoop is an open-source implementation of MapReduce Model. The cluster computation resources are divided into map slots and reduce slots, which are configured by Hadoop administrator in advance. A MapReduce job generally consists of map tasks and reduce tasks. Map tasks have to be allocated with map slots, and reduce tasks have to be allocated with reduce slots. 4

5. Hadoop Execution Model 5 Map slotsReduce slots Map tasks start before reduce tasks Map tasks can only run on map slots, reduce tasks can only run on reduce slots Implication: Slots utilization can be poor for MapReduce Workloads under the current static slot configuration and allocation policy!!!

6. Our Goals To maximize the slot resource utilization for Hadoop cluster without any prior knowledge or assumption about MapReduce jobs. In other words, we want to achieve that at any time there should be no idle map/reduce slots available when there are pending tasks, i.e., trying to make slots as busy as possible. Our work focuses on Hadoop Fair Scheduler, i.e., improving the performance while guaranteeing fairness. 6

7. OutLine Background & Motivations DHFS Evaluation Conclusion 7

8. Our Approach We propose a dynamic slot allocation technique by breaking the existing slot allocation constrain: 1). Slots are generic and can be used by map and reduce tasks. 2). Map Tasks prefer to use map slots and likewise reduce tasks prefer to use reduce slots. In other words, Case 1:, no slot borrow is needed. Case 2:, borrow reduce slots for map tasks. Case 3:, borrow map slots for reduce tasks. Case 4:, no slot borrow is needed. 8

9. Dynamic Hadoop Fair Scheduler (DHFS) We provide two types of DHFS, based on different levels of fairness.  Pool-Independent DHFS (PI-DHFS)  Pool-dependent DHFS (PD-DHFS) Each MapReduce pool consists of two sub-pools:  Map-phase pool  Reduce-phase pool 9

10. PI-DHFS It’s subject to the ‘fairness’ concept of default Hadoop Fair Scheduler, i.e., fair share is done across phase-pools within a phase. The dynamic allocation process consists of two parts:  Intra-phase dynamic slot allocation  Inter-phase dynamic slot allocation 10

11. PI-DHFS It will compute Intra-phase dynamic slot allocation first, and then Inter-phase dynamic slot allocation. 11

12. PD-DHFS Fair share is done across pools, instead of phase. The dynamic allocation process consists of two parts:  Intra-pool dynamic slot allocation  Inter-pool dynamic slot allocation 12

13. PD-DHFS It will compute Intra-pool dynamic slot allocation first, and then Inter- pool dynamic slot allocation. 13

14. Overview of Slot Allocation Flow The slot allocation flow for each pool under PD-DHFS. 14 Reduce task assignment Map task assignment Pending map tasks and idle map slots? Pending reduce tasks and idle reduce slots? Pending map tasks? Pending reduce tasks? (4) (2) (1) (3) Yes No Yes No Yes No

15. OutLine Background & Motivations DHFS Evaluation Conclusion 15

16. Experimental Setup Enviroments  A Hadoop cluster consisting of 10 nodes, each with two Intel X5675 CPUs, 24GB memory and 56GB hard disks. Workloads  Tested Workload. It is a mix of three representative applications, WordCount, Sort, Grep, with Wikipedia article history dataset of different sizes, e.g., 10 GB, 20GB, 30GB, 40GB. 16

17. Execution Process for DHFS 17

18. Performance Improvement 18

19. Performance Improvement Under Different Percentages of Borrowed Map and Reduce Slots 19

20. OutLine Background & Motivations DHFS Evaluation Conclusion 20

21. Conclusion Current static slot configuration and allocation policy can make slot utilization poor. Two DHFSs (PI-DHFS, PD-DHFS) are proposed to address the slot utilization problem for Hadoop Fair Scheduler. Experimental results show that DHFS improves the performance of MapReduce workloads significantly while guaranteeing the fairness. The source code of DHFS is available at: http://sourceforge.net/projects/dhfs/ 21

22. Acknowledgement This work is supported by the ”User and Domain driven data analytics as a Service framework” project under the A*STAR Thematic Strategic Research Programme (SERC Grant No. 1021580034). Bingsheng He was partly supported by a startup Grant of Nanyang Technological University, Singapore. 22

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