Buffer Management Policy

1. Buffer Management Policy TANG Xian

2. Outline • Introduction • Buffer management policy on disk • Buffer management policy on flash • Conclusion

3. Introduction • Buffer management is very important for the overall performance of the DBMS A. Leventhal. Flash Storage Memory. Communications of ACM, July 2008

4. Magnetic disk The same speed of Read/Write Rewrite in place Mechanical moving parts Buffer hit ratio Flash Asymmetric speed of Read/Write No overwrite No mechanics delay Try to reduce the number of write/erase at the expense of the read operations Introduction

5. Outline • Introduction • Buffer management policy on disk • Buffer management policy on flash • Conclusion

6. LRU • Replaces the least recently used page • Captures recency but not frequency 0 1 2 3 2 3 2 1 2 1 3 2 3 2 2 3 2 2 3 1 0 3 1 Richard L. Mattson, Jan Gecsei, Donald R. Slutz, Irving L. Traiger: Evaluation Techniques for Storage Hierarchies. IBM Systems Journal (IBMSJ) 9(2):78-117 (1970)

7. LFU • Replaces the least frequently used page • Captures frequency but not recency 0 3 0 0 0 1 1 2 3 1 0 2 3 0 1 2 3 3 2 1 Alfred V. Aho, Peter J. Denning, Jeffrey D. Ullman: Principles of Optimal Page Replacement. J. ACM (JACM) 18(1):80-93 (1971)

8. 7 6 3 Page number 7 5 5 1 8 0 11 2 0 9 3 2 1 4 4 9 6 8 F F F T New flag T T T T F F F F T F F F F T T F T 1 1 1 1 1 1 1 1 1 1 count 1 2 1 1 1 1 1 1 2 2 1 F F T F F F T T T F T Old flag F T F F F F F F F F MRU LRU New section middle section old section New boundary old boundary FBR 0, 7, 11 0, 7, 11 0, 7, 11 0, 7, 11 F T MRU LRU 2 New section middle section old section New boundary old boundary F T John T. Robinson, Murthy V. Devarakonda: Data Cache Management Using Frequency-Based Replacement. SIGMETRICS 1990:134-142

9. Ain Am 2Q 8, 16, 2, 19, 3 8, 16, 2, 19, 3 8, 16, 2, 19, 3 • Ain: FIFO • Aout: FIFO • Am: LRU head tail 5 10 2 15 1 18 Aout 13 16 8 5 7 6 4 3 11 9 0 25% Theodore Johnson, Dennis Shasha: 2Q: A Low Overhead High Performance Buffer Management Replacement Algorithm. VLDB 1994:439-450

10. Ain Am 2Q 8, 16, 2, 19, 3 • Ain: FIFO • Aout: FIFO • Am: LRU head tail 8 10 2 15 1 5 Aout 2 16 13 8 7 6 4 3 11 9 0 25% Theodore Johnson, Dennis Shasha: 2Q: A Low Overhead High Performance Buffer Management Replacement Algorithm. VLDB 1994:439-450

11. 16 13 2 7 6 4 3 11 9 Ain Am 2Q 8, 16, 2, 19, 3 • Ain: FIFO • Aout: FIFO • Am: LRU head tail 8 10 15 1 5 Aout 19 0 25% Theodore Johnson, Dennis Shasha: 2Q: A Low Overhead High Performance Buffer Management Replacement Algorithm. VLDB 1994:439-450

12. 2 7 6 4 Ain Am 2Q • Ain: FIFO • Aout: FIFO • Am: LRU 8, 16, 2, 19, 3 head tail 8 10 15 1 5 Aout 19 16 13 3 11 9 25% Theodore Johnson, Dennis Shasha: 2Q: A Low Overhead High Performance Buffer Management Replacement Algorithm. VLDB 1994:439-450

13. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 CLOCK (1) • All the resident pages are placed around a circular list, like a clock; • Each page is associated with a reference bit, indicating if the page has been accessed. CLOCK hand On a HIT Set Reference bit to 1 (no algorithm operations) F. J. Corbato. “A Paging Experiment with the Multics System,” Project MAC Memo MAC-M-384, Mass. Inst. Of Tech., 1968

14. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 CLOCK (2) • Starts from the currently pointed page, and evicts the page if it is”`0”; • Move the clock hand until reach a “0” page; • Give “1” page a second chance, and reset its “1” to “0” On a sequence of two MISSes CLOCK hand F. J. Corbato. “A Paging Experiment with the Multics System,” Project MAC Memo MAC-M-384, Mass. Inst. Of Tech., 1968

15. Outline • Introduction • Buffer management policy on disk • Buffer management policy on flash • Conclusion

16. CFLRU • Clean-first LRU 9 1 D 9 C 2 C 3 D 4 D 5 C 6 D 7 C 8 D Working region Clean-first region Seon-Yeong Park, Dawoon Jung, Jeong-Uk Kang, Jinsoo Kim, Joonwon Lee: CFLRU: a replacement algorithm for flash memory. CASES 2006:234-241

17. CFLRU • Clean-first LRU 9 0 9 C 0 C 1 D 2 C 3 D 4 D 5 C 6 D 8 D Working region Clean-first region Seon-Yeong Park, Dawoon Jung, Jeong-Uk Kang, Jinsoo Kim, Joonwon Lee: CFLRU: a replacement algorithm for flash memory. CASES 2006:234-241

18. CFLRU • Clean-first LRU 9 0 7 0 C 9 C 1 D 2 C 3 D 4 D 6 D 8 D Working region Clean-first region Seon-Yeong Park, Dawoon Jung, Jeong-Uk Kang, Jinsoo Kim, Joonwon Lee: CFLRU: a replacement algorithm for flash memory. CASES 2006:234-241

19. CFLRU/C, CFLRU/E, DL-CFLRU/E • CFLRU: • p7 , p5 , p8 , p6 • CFLRU/Count: • w.clean  LRU • w.dirty  LFU • p7 , p5 , + LFU (p8, p6) • CFLRU/Erase: • w.clean  LRU • w.dirty block with the lowest erase count • p7 , p5 , + block erase count (p8, p6) • DL-CFLRU/E (Double List CFLRU/E): • buffer.clean  LRU • w.dirty  block with the lowest erase count • p7, p5, p4, p2, + block erase count (p8, p6) Yun-Seok Yoo, Hyejeong Lee, Yeonseung Ryu, Hyokyung Bahn: Page Replacement Algorithms for NAND Flash Memory Storages. ICCSA 2007:201-212

20. LRU Head LRU Tail LRU Head LRU Tail FAB • Portable Media Player (PMP) • A block-level LRU policy • Reduce GC cost Heeseung Jo, Jeong-Uk Kang, Seon-Yeong Park, Jin-Soo Kim, and Joonwon Lee. FAB: flash-aware buffer management policy for portable media players. Consumer Electronics, IEEE Transactions on, 52(2):485-493, 2006

21. LRU Head LRU Tail BPLRU • Block-level LRU • Page padding Hyojun Kim and Seongjun Ahn. BPLRU: A Buffer Management Scheme for Improving Random Writes in Flash Storage, FAST 2008

22. Outline • Introduction • Buffer management policy on disk • Buffer management policy on flash • Conclusion

23. Conclusion • 6 buffer management policies on disk • Hit ratio • Recency • frequency • 4 buffer management policies on flash • Reduce write operation • Page-level • Block-level

24. Q & A • Thanks!