Chunking Algorithm Fast SIMD-Based

Fast SIMD-Based Chunking AlgorithmPSC 2019-Aug-27 Johnny Dude

Fast SIMD-BasedFast SIMD-BasedChunking AlgorithmChunking Algorithm

Yehonatan Dude, Michael Hirsch, Yair Toaff

PSC 2019PSC 2019


OutlineOutline

1. Background2. Chunking Problem3. Traditional Solutions4. Our Solution5. Future Work



Background - DeduplicationBackground - Deduplication

Deduplication is a technique for eliminatingDeduplication is a technique for eliminatingduplicate copies of repeating data.duplicate copies of repeating data.



Deduplication process in a nutshellDeduplication process in a nutshell1. Divide into chunks2. Calculate the chunks' hashes3. Store chunks uniquely


Object 1

Object 2


A BC

D BC

D DObject 1

Object 2


A BC

D BC

D DObject 1

Object 2

Object 1Object 2

AB

CD

hA

hB

hC

hD

hA hBhC hDhD

hBhD hC


Background - Chunking MethodsBackground - Chunking Methods

How to chunk the input dataHow to chunk the input data1. Simple - fixed size.2. Content aware - files, objects, applications.3. Content sensitive - rolling hash.



The Opera ghost really existed._ He was not, as was long believed

, a creature of the imagination_ of the artists, the superstition

of the managers, or a product o f the joy and impressionable bra

ins of the young ladies of the b allet, their mothers, the box-ke

epers, the cloak-room attendants or the concierge. Yes, he exist

ed in flesh and blood, although_ he assumed the complete appearan

ce of a real phantom; that is to say, of a spectral shade.

The Opera ghost really existed._ He was not, as was long believed

, a creature of the imagination_ of the artists, the superstition

of the managers, or a product o f the absurd and impressionable

brains of the young ladies of th e ballet, their mothers, the box

-keepers, the cloak-room attenda nts or the concierge. Yes, he ex

isted in flesh and blood, althou gh he assumed the complete appea

rance of a real phantom; that is to say, of a spectral shade.


The Opera ghost really existed.

He was not, as was long believed, a creature of the imagination of the

artists, the superstition of the managers, or a product of the joy and

impressionable brains of the young ladies of the ballet, their

mothers, the box-keepers, the cloak-room attendants or the concierge.

Yes, he existed in flesh and blood, although he assumed the complete

appearance of a real phantom; that is to say, of a spectral shade.

The Opera ghost really existed.

He was not, as was long believed, a creature of the imagination of the

artists, the superstition of the managers, or a product of the absurd

and impressionable brains of the young ladies of the ballet, their

mothers, the box-keepers, the cloak-room attendants or the concierge.

Yes, he existed in flesh and blood, although he assumed the complete

appearance of a real phantom; that is to say, of a spectral shade.


The Opera ghost really existed. He was not, as was long believed

, a creature of the imagination of the artists, the superstition

of the managers, or a product of the joy and impressionable bra

ins of the young ladies of the ballet, their mothers, the box-ke

epers, the cloak-room attendants or the concierge. Yes, he exist

ed in flesh and blood, although he assumed the complete appearan

ce of a real phantom; that is to say, of a spectral shade.

The Opera ghost really existed. He was not, as was long believed

, a creature of the imagination of the artists, the superstition

of the managers, or a product of the absurd and impressionable

brains of the young ladies of the ballet, their mothers, the box

-keepers, the cloak-room attendants or the concierge. Yes, he ex

isted in flesh and blood, although he assumed the complete appea

rance of a real phantom; that is to say, of a spectral shade.


Background - Deduplication PerformanceBackground - Deduplication Performance

In 2017 we worked on a deduplication engine,and we tried to improve its performance.



Seconds per GB

LZ4

Karp-Rabin

SHA1

Other1 2


Chunking ProblemChunking Problem

Given a stream of bytes, divide it into chunks for deduplication.1. Output identical chunks for identical data2. Good chunk size distribution.3. Good performance.4. Works for any input (photo, DB, text, random, etc...)



Traditional SolutionsTraditional Solutions

Karp-RabinCyclic Polynomial



●●● Xk-2 Xk-1 Xk=Hash( )Hk

Criteria(If Hk ) holds then mark a boundary after Xk

Xk-63 Xk-62 Xk-61


Xk-62 Xk-61 Xk-60 ●●● Xk-1 Xk Xk+1=Hash( )HK+1

Xk-63 Xk-62 Xk-61 ●●● Xk-2 Xk-1 Xk=Hash( )Hk


Xk-62 Xk-61 Xk-60 ●●● Xk-1 Xk Xk+1=Hash( )HK+1

Xk-63 Xk-62 Xk-61 ●●● Xk-2 Xk-1 Xk=Hash( )Hk

=RollHash( Xk-63 Xk+1Hk ), ,


Karp-Rabin Cyclic Polynomial


Proposed SolutionProposed Solution

How does it work:How does it work:1. Work with rolling vectors2. Calculate a hash of byte size3. Calculate the criteria, in a way that:

Number of calculations are constantunrelated to the vector sizeCan find a cutting point at a byte offset



Xk-62

Xk-61

Xk-60

●●● Xk-10 Xk-6 Xk-2=Hash( )hk-2

Xk-63 Xk-59

Xk-58

●●● Xk-11 Xk-7 Xk-3=Hash( )hk-3

Xk-57

Xk-56

Xk-55

Xk-54

Xk-53

Xk-52

●●● Xk-9 Xk-5 Xk-1 )

●●● Xk-8 Xk-4 Xk )=Hash(hk

=Hash(hk-1


●●● Xk+2=Hash( )hk+2

Xk-59

Xk-58

●●● Xk+1=Hash( )hk+1

Xk-57

Xk-56

Xk-55

Xk-54

Xk-53

Xk-52

●●● Xk+3 )

●●● Xk+4 )=Hash(hk+4

=Hash(hk+3

=RollHash( ), ,

Xk-2

Xk-3

Xk-1

Xk

=RollHash( ), ,

=RollHash( ), ,

=RollHash( ), ,

hk-2

hk-3

hk

hk-1

Xk-62

Xk-61

Xk-60

Xk-63

Xk+2

Xk+1

Xk+3

Xk+4


= Criteria( Hk )ck

= Criteria( Hk+1 )ck+1



Pass

Fail

Pass

Pass


= Criteria( Hk )ck




0 1 0 0

ck ...ck+3

Pass

Fail

Pass

Pass


1 1 0 0

ck-4 ...ck-1

0 1 0 0

ck ...ck+3

0 0 0 1

ck+4 ...ck+7


1 1 0 0

ck-4 ...ck-1

0 1 0 0

ck ...ck+3

0 0 0 1

ck+4 ...ck+7

Trailing Zeroes

Leading Zeroes


1 1 0 0

ck-4 ...ck-1

0 1 0 0

ck ...ck+3

0 0 0 1

ck+4 ...ck+7

Trailing Zeroes

Leading Zeroes

Boundary


Measured ResultsMeasured Results



Algorithm Random Data Corpus Data

Karp-Rabin 975 MB/s 927 MB/s

Cyclic-Polynomial 1675 MB/s 1676 MB/s

Ours 6715 MB/s 7136 MB/s


ChunkingAlg.

DedupPerf.

LZ4 SHA1 Other Chunking

Karp-Rabin 262 MB/s 63.9% 4.1% 3.8% 28.1%

Ours 345 MB/s 84.5% 5.4% 5.1% 4.7%


Same DistributionFaster Chunking PerformanceFaster Overall Performance


Future WorkFuture Work

A chunking algorithm that is* Past Presented Future

Backward Compatible N/A f(k, x) ≠ f(l, x) f(k, x) = f(l, x)

Work cn cn cn

Speed cn c(n log k) / k c(n log k) / k



ThanksThankshttps://github.com/dudejohnny/PSC2019

https://github.com/dudejohnny/PSC2019

Chunking Algorithm Fast SIMD-Based

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