1.
Papers We Love:
ARC after dark
CTO
bryan@joyent.com
Bryan Cantrill
@bcantrill

2.
Papers we love: ARC
• Discussing ARC: A self-tuning, low overhead replacement
cache by Nimrod Megiddo and Dharmendra Modha
• Appeared in USENIX FAST ’03
• Has been broadly deployed in production — most notably in
ZFS, in at least illumos (SmartOS, etc.) and FreeBSD
• As much as possible, want to let the paper speak for itself —
and provoke discussion!

3.
ARC in the abstract

4.
Introduction

5.
Book of Genesis, 1:1

6.
The Von Neumann architecture

7.
“The Memory Organ”

8.
“Entirely impractical”

9.
The problem

10.
Main themes

11.
Related work: Optimal

12.
Related work: Using recency with LRU

13.
Related work: Using frequency with LFU

14.
Related work: LRU-2

15.
Related work: LRFU

16.
Related work: ALRFU (AYFKM?!)

17.
Related work: MQ

18.
Related work: MQ, cont.

19.
Related work: “Multiple experts”

20.
Related work: Ghost caches

21.
Generic cache replacement policy (?)

22.
Fixed replacement cache

23.
Adaptive replacement cache

24.
Adaptive replacement cache

25.
Adaptive replacement cache

26.
Adaptive replacement cache

27.
Adaptive replacement cache

28.
Adaptive replacement cache

29.
Adaptive replacement cache

30.
ARC performance

31.
ARC performance

32.
ARC performance

33.
ARC performance vs. LRU

34.
ARC performance vs. FRC offline

35.
ARC performance: “Empirically universal”

36.
ARC performance: p over time

37.
ARC: Conclusions

38.
ARC: Endnotes

39.
ARC: Endnotes

40.
ARC: Epilogue
• The ARC is the basis of the cache used by ZFS, with many
enhancements over time:
• Variable sized buffers — though now returning to be fixed
blocks with ARC buffer data (ABD)
• L2ARC to allow SSDs to be used as a cache
• Separate metadata lists
• Compressed ARC
• A challenge has been to make all of ARC variable-sized…

41.
Peril of a variably-sized ARC!