Buffer Management Policy

TANG Xian

Outline

• Introduction

• Buffer management policy on disk

• Buffer management policy on flash

• Conclusion

Introduction

• Buffer management is very important for the overall performance of the DBMS

A. Leventhal. Flash Storage Memory. Communications of ACM, July 2008

Introduction

• 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

Outline

• Introduction

• Buffer management policy on disk

• Buffer management policy on flash

• Conclusion

LRU

• Replaces the least recently used page

• Captures recency but not frequency

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)

0 1 2 3 2 3 2 1

0

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1

LFU

• Replaces the least frequently used page

• Captures frequency but not recency

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23

0

Alfred V. Aho, Peter J. Denning, Jeffrey D. Ullman: Principles of Optimal Page Replacement. J. ACM (JACM) 18(1):80-93 (1971)

123

32

3

FBR

John T. Robinson, Murthy V. Devarakonda: Data Cache Management Using Frequency-Based Replacement. SIGMETRICS 1990:134-142

Page number

Newflag

count

Oldflag

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0, 7, 11

MRU LRU

New section middle section old section

2T F

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MRU LRU

New section middle section old section

0, 7, 110, 7, 110, 7, 11

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2Q• Ain: FIFO• Aout: FIFO• Am: LRU

Theodore Johnson, Dennis Shasha: 2Q: A Low Overhead High Performance Buffer Management Replacement Algorithm. VLDB 1994:439-450

13 8 5 07 6 4 3 11 9

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Ain Am

head tail

8, 16, 2, 19, 38, 16, 2, 19, 3

25%

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2Q8, 16, 2, 19, 3

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Ain Am

head tail

25%

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2

• Ain: FIFO• Aout: FIFO• Am: LRU

Theodore Johnson, Dennis Shasha: 2Q: A Low Overhead High Performance Buffer Management Replacement Algorithm. VLDB 1994:439-450

2Q8, 16, 2, 19, 3

0

10 15 1Aout

Ain Am

head tail

25%

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1316 7 6 4 3 11 9219

• Ain: FIFO• Aout: FIFO• Am: LRU

Theodore Johnson, Dennis Shasha: 2Q: A Low Overhead High Performance Buffer Management Replacement Algorithm. VLDB 1994:439-450

2Q

8, 16, 2, 19, 3

10 15 1Aout

Ain Am

head tail

25%

58

1316 3 11 97 6 4219

• Ain: FIFO• Aout: FIFO• Am: LRU

Theodore Johnson, Dennis Shasha: 2Q: A Low Overhead High Performance Buffer Management Replacement Algorithm. VLDB 1994:439-450

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.

On a HITSet Reference bit to 1

(no algorithm operations)

0

CLOCK hand

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01100

01

1

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11 0 0

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10

F. J. Corbato. “A Paging Experiment with the Multics System,” Project MAC Memo MAC-M-384, Mass. Inst. Of Tech., 1968

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

0

CLOCK hand

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01100

01

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F. J. Corbato. “A Paging Experiment with the Multics System,” Project MAC Memo MAC-M-384, Mass. Inst. Of Tech., 1968

Outline

• Introduction

• Buffer management policy on disk

• Buffer management policy on flash

• Conclusion

CFLRU

• Clean-first LRU

1D

2C

3D

4D

5C

6D

7C

8D

9

9C

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

CFLRU

• Clean-first LRU

1D

2C

3D

4D

5C

6D

8D

9

9C

Working region Clean-first region

0

0C

Seon-Yeong Park, Dawoon Jung, Jeong-Uk Kang, Jinsoo Kim, Joonwon Lee: CFLRU: a replacement algorithm for flash memory. CASES 2006:234-241

CFLRU

• Clean-first LRU

1D

2C

3D

4D

6D

8D

9

9C

Working region Clean-first region

0

0C

7

Seon-Yeong Park, Dawoon Jung, Jeong-Uk Kang, Jinsoo Kim, Joonwon Lee: CFLRU: a replacement algorithm for flash memory. CASES 2006:234-241

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

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

LRU

HeadLRU

Tail

LRU

HeadLRU

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

LRU

HeadLRU

Tail

Outline

• Introduction

• Buffer management policy on disk

• Buffer management policy on flash

• Conclusion

Conclusion

• 6 buffer management policies on disk– Hit ratio

• Recency• frequency

• 4 buffer management policies on flash– Reduce write operation

• Page-level• Block-level

• Q & A

• Thanks!