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. Introduction Magnetic disk Flash 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

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 1 2 3 2 3 2 1 3 3 2 2 2 1 2 2 3 1 3 2 1 3
Richard L. Mattson, Jan Gecsei, Donald R. Slutz, Irving L. Traiger: Evaluation Techniques for Storage Hierarchies. IBM Systems Journal (IBMSJ) 9(2): (1970)

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

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

9. 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 16 13 8 5 7 6 4 3 11 9
Ain Am
25%
Theodore Johnson, Dennis Shasha: 2Q: A Low Overhead High Performance Buffer Management Replacement Algorithm. VLDB 1994:

10. 2Q 8, 16, 2, 19, 3 Ain: FIFO Aout: FIFO Am: LRU head tail 8 5 10 2 1513 8 7 6 4 3 11 9
Ain Am
25%
Theodore Johnson, Dennis Shasha: 2Q: A Low Overhead High Performance Buffer Management Replacement Algorithm. VLDB 1994:

11. 2Q Ain: FIFO 8, 16, 2, 19, 3 Aout: FIFO Am: LRU head tail 8 5 10 15 113 16 7 6 4 3 11 9 2 19
Ain Am
25%
Theodore Johnson, Dennis Shasha: 2Q: A Low Overhead High Performance Buffer Management Replacement Algorithm. VLDB 1994:

12. 2Q Ain: FIFO Aout: FIFO 8, 16, 2, 19, 3 Am: LRU head tail 8 5 10 15 113 7 6 4 2 3 11 9
Ain Am
25%
Theodore Johnson, Dennis Shasha: 2Q: A Low Overhead High Performance Buffer Management Replacement Algorithm. VLDB 1994:

13. (no algorithm operations)
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. 1 1 1 1
CLOCK hand 1
On a HIT
Set Reference bit to 1
(no algorithm operations) 1 1 1
F. J. Corbato. “A Paging Experiment with the Multics System,” Project MAC Memo MAC-M-384, Mass. Inst. Of Tech., 1968 1

14. On a sequence of two MISSes
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” 1 1 1
On a sequence of two MISSes 1
CLOCK hand
On a miss access, CLOCK turns the clock hand, evict the first “0” page;
CLOCK inserts the missed page at the head, initialize its reference bit to 0.
If the ref-bit of page pointed by the hand is “1”, CLOCK gives it a second chance without replacing it,
And reset its “1” to “0” and continue to look for a page with its bit of “0”
CLOCK simulates LRU replacement very well, and its hit ratios are very close to LRU. 1 1 1 1
F. J. Corbato. “A Paging Experiment with the Multics System,” Project MAC Memo MAC-M-384, Mass. Inst. Of Tech., 1968 1

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:

17. CFLRU Clean-first LRU 9 9 C C 1 D 2 C 3 D 4 D 5 C 6 D 8 D9 C 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:

18. CFLRU Clean-first LRU 9 7 C 9 C 1 D 2 C 3 D 4 D 6 D 8 D Working region7 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:

19. CFLRU/C, CFLRU/E, DL-CFLRU/E
p7 , p5 , p8 , p6
CFLRU/Count:
w.clean  LRU
w.dirty  LFU
p7 , p5 , + LFU (p8, p6)
CFLRU/Erase:
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:

20. FAB Portable Media Player (PMP) A block-level LRU policy
Reduce GC cost
LRU
Head
Tail
LRU
Head
Tail
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): , 2006

21. BPLRU Block-level LRU Page padding LRU Head Tail
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!