Towards Efficient, Portable Application-Level Consistency

File System C

Ext3-ordered: Safest for app
Safe new file: Manpages explici

ext3 – ordered Safe Ordered
rename appends
ext3 –
writeback  
ext4 – ordered 

ext4 –original 

Btrfs 

Comparison

plications
itly warn against this property.

Ordered dir- Safe Safe new
ops appends file

  



 
 



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Out

• Background:Application
• Goals, Methodology of S
• File System Behavior
• ALC Bugs
• ALC Performance
• Summary

tline

n-Level Consistency (ALC)
Study

27

Bugs: LevelDB

• LevelDB is a key-value d
• Put(key, value, synchrono

– Atomic
– Ordered

• If a Put() can be retrieve
retrieved

– Synchronous = true: Dur
– No corruption

B Guarantees

database
ous)

ed, all previous Put() can also be

rable

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Bugs: Guar
Post-Crash

Post-Crash Property Le

Ordered append Re

Ordered directory operations Re

Safe new file Co

Safe rename Co

rantees vs
Properties

evelDB Guarantee Affected
e-ordering, Corruption
e-ordering, Corruption
orruption
orruption (Previously fixed bug)

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Out

• Background:Application
• Goals, Methodology of S
• File System Behavior
• ALC Bugs
• ALC Performance
• Summary

tline

n-Level Consistency (ALC)
Study

30

Performance O

• SQLite:

“In particular, we suspect t
exhibit the safe append pr
might support atomic sect
known for certain, SQLite
approach and assume the

• Five configuration opti
• Evaluated performance

– On top of ext3 - order

Optimizations

that most modern filesystems
roperty and that many of them
tor writes. But until this is
e will take the conservative
worst.”

ions
e for each option

red

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Performance: SQLit

Normalized Throughput 4 Ext3-
3.5
Safe S
3 appends
2.5
Configu
2
1.5

1
0.5

0
Atomic
writes

te – Configurations

-ordered: 40 to 50% improvement
250 % improvement
with data journaling

Sequential Power-safe Sync
directory
writes overwrites

uration options

32

Out

• Background:Application
• Goals, Methodology of S
• File System Behavior
• ALC Bugs
• ALC Performance
• Summary

tline

n-Level Consistency (ALC)
Study

33

Summ

• Bugs

– Four new bugs in Level
– Past bugs: One in Level
– All bugs exposed on so

• Performance

– Wildly differing perform
exact file system behav

mary

lDB
lDB, three in SQLite
ome file system

mance when optimized for
vior

34

Concl

• State of the art: For ef
consistency, application
specific details of file s

lusion

ffective application-level
n developers depend on
system implementation

35

Thank
Questions or

k you!
r suggestions?

36