1/20 SIGMOD 2011Turbocharging the DBMS Buffer Pool using an SSD Microsoft Jim Gray Systems Lab ...

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SIGMOD 2011 Turbocharging the DBMS Buffer Pool using an SSD

Microsoft Jim Gray Systems Lab & University of Wisconsin, Madison

Turbocharging the DBMS Buffer Pool using an SSD

Jaeyoung Do, Donghui Zhang, Jignesh M. Patel,David J. DeWitt, Jeffrey F. Naughton, Alan Halverson

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Memory Hierarchy

DRAM

HDDDisk

For over three decades…

Now: a disruptive change…

SSD

??

SSD wisdom:- Store hot data.- Store data with

random-I/O access.

Fast random I/Os; but expensive.

Cache

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Take Home Message• Use an SSD to extend the Buffer Pool.• Implemented in Microsoft SQL Server

2008R2.• Evaluated with TPC-C, E, and H.• Up to 9X speedup.

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Prior Art• [Holloway09] A. L. Holloway. Chapter 4: Extending the Buffer

Pool with a Solid State Disk. In Adapting Database Storage for New Hardware, UW-Madison Ph.D. thesis, 2009.

• [KV09] Koltsidas and Viglas. The Case for Flash-Aware Multi-Level Caching. University of Edinburgh Technical Report, 2009.

• [KVSZ10] B. M. Khessib, K. Vaid, S. Sankar, and C. Zhang. Using Solid State Drives as a Mid-Tier Cache in Enterprise Database OLTP Applications. TPCTC’10.

• [CMB+10] M. Canim, G. A. Mihaila, B. Bhattacharjee, K. A. Ross, and C. A. Lang. SSD Bufferpool Extensions for Database Systems. In VLDB’10.

State-of-the-art:Temperature-Aware Caching (TAC)

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Research Issues• Page flow• SSD admission policy• SSD replacement policy• Implication on checkpoint

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Implemented Designs

• Temperature-Aware Caching (TAC)• Dual-Write (DW)• Lazy-Cleaning (LC)

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Page Flow

BP Operations:read evict read modify evict

TAC writes a clean page to the SSD right after reading from the disk.

C

Buffer pool

Disk SSD BP

C

C

C

Buffer pool

Disk SSD BP

C

C

Buffer pool

Disk SSD BP

C

TAC Dual-Write Lazy-Cleaning

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Page Flow


C

Buffer pool

Disk SSD BP

C

C

C

Buffer pool

Disk SSD BP

C

C

Buffer pool

Disk SSD BP

C

DW/LC writes a clean page to the SSD upon eviction from BP.

C C

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Page Flow


C

Buffer pool

Disk SSD BP

C

C

C

Buffer pool

Disk SSD BP

C

C

Buffer pool

Disk SSD BP

C

Read from the SSD: same for all.

C C

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CCC


Page Flow


Buffer pool

Disk SSD BP

C

CBuffer pool

Disk SSD BP

CBuffer pool

Disk SSD BP

C

Upon dirtying a page, TAC does notreclaim the SSD frame.

C CI

D D D

I I

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D

D D D

I

Page Flow


Buffer pool

Disk SSD BP

C

Buffer pool

Disk SSD BP

Buffer pool

Disk SSD BP

Upon evicting a dirty page:- TAC and DW are write through;- LC is write back.

CI

Lazy cleaning

C

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SSD Admission/Replacement Policies• TAC

– Admission: if warmer than the coldest SSD page.– Replacement: the coldest page.

• DW/LC– Admission: if loaded from disk using a random I/O.– Replacement: LRU2.

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Implication on Checkpoint• TAC/DW

– No change, because every page in the SSD is clean.• LC

– Needs change, to handle the dirty pages in the SSD.

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Experimental SetupConfiguration

Machine HP Proliant DL180 G6 Server

Processor Intel® Xeon® L5520 2.27GHz (dual quad core)

Memory 20GB

Disks 8X SATA 7200RPM 1TB

SSD 140GB Fusion ioDrive 160 SLC

OS Windows Server 2008 R2

DBMS SQL Server 2008 R2

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TPC-C

100G

B

200G

B

400G

B0

2

4

6

8

10

TAC DW LC

SpeedupRelative to

noSSD

Q: Why is LC so good?A: Because TPC-C is update

intensive. In LC, dirty pages in the SSD are frequently re-referenced.

83% of the SSD references are to dirty SSD pages.

LC is 9X better than noSSD, or 5X better than DW/TAC.

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TPC-E

100G

B

200G

B

400G

B0

2

4

6

8

10

TAC DW LC

SpeedupRelative to

noSSD

Q: Why do the three designs have similar speedups?

A: Because TPC-E is read intensive.

Q: Why does the highest speedup occur for 200GB database?

A: For 400GB, a smaller fraction of data is cached in the SSD;For 100GB, a larger fraction of data is cached in the memory BP.

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TPC-H

45GB 160GB0

2

4

6

8

10

TAC DW LC

SpeedupRelative to

noSSD

Q: Why are the speedups smaller than in C or E?

A: Because most I/Os are sequential.For random I/Os: Fusion is 10X faster;For sequential I/Os: 8x disks are 1.4X faster.

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Disks are the Bottleneck

As long as disks are the bottleneck…Using less expensive SSDs may be good enough.

8 Disks

0.00 1.30 2.60 3.90 5.20 6.50 7.80 9.100

10

20

30

40

50readwrite

Time (hours)

I/O B

andw

idth

(MB

/s)

0.001.302.603.905.206.507.809.100

10

20

30

40

50readwrite

Time (hours)

I/O B

andw

idth

(MB

/s)

SSD

capacityreached!

about half capacity

I/O traffic to the disks and SSD, for TPC-E 200GB.

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Long Ramp-up Time

If restarts are frequent…Restart from the SSD may reduce rampup time.

0.001.202.403.604.806.007.208.409.600

20

40

60

80

100

120 TAC DW LC

Time (#hours)

tpsE (#

trans/ sec)

TPC-E (200GB) Q: Why does rampup take 10 hours?

A: Because the SSD is being filled slowly, gated by the random read speed of the disks.

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Conclusions

• SSD buffer pool extension is a good idea.– We observed a 9X speedup (OLTP) and a 3X speedup (DSS).

• The choice of design depends on the update frequency.– For update-intensive (TPC-C) workloads: LC wins.– For read-intensive (TPC-E or H) workloads: DW/LC/TAC have similar

performance.• Mid-range SSDs may be good enough.

– With 8 disks, only half of FusionIO’s bandwidth is used.• Caution: rampup time may be long.

– If restarts are frequent, the DBMS should restart from the SSD.

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Backup Slides

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Architectural Change

Buffer Manager

I/O Manager

Disk

BPBuffer Manager

I/O Manager

Disk

SSD Manager

SSD BP

BP

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Data Structures

SSD Buffer PoolSSD

Memory

C D C C DSSD Buffer TableSSD Free List

SSD Hash Table

C C C D DSSD Heap Array

Clean Heap Dirty Heap

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Further Issues

• Aggressive filling• SSD throttle control• Multi-page I/O request• Asynchronous I/O handling• SSD partitioning• Gather write

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