Presentation on theme: "ARC: A self-tuning, low overhead Replacement Cache"— Presentation transcript:
1 ARC: A self-tuning, low overhead Replacement Cache Nimrod Megiddo andDharmendra S. ModhaPresented by Gim Tcaesvk
2 Cache Cache is expensive. The replacement policy is the only algorithm of interest.
3 Cache management problem Maximize the hit rate.Minimize the overhead.ComputationSpace
4 Belady’s MIN Replaces the furthest referenced page. Optimum for every case.Provides upper bound of hit ratio.But,Who knows the future?
5 LRU (Least Recently Used) Replaces the least recently used page.Optimum policy for SDD (Stack Depth Distribution).Captures recency but not frequency.232132232231123232113
6 LFU (Least Frequently Used) Replaces the least frequently used page.Optimum policy for IRM (Independent Reference Model).Captures frequency but not recency.11123321
7 Drawbacks of LFU Logarithmic complexity in cache size High frequently used page is hardly to paged out.Even if it is no longer useful.
8 LRU-2 Replaces the least 2nd recently used page. Optimum online policy which knows at most 2 most recent reference for IRM.
9 Limitations of LRU-2 Logarithmic complexity Tunable parameter, Due to priority queueTunable parameter,CIP (Correlated Information Period)2(2,4)1(1,3)0(-∞,0)
10 2Q (modified LRU-2)Uses simple LRU list instead of the priority queue.Two parameter, Kin and KoutKin=Correlated Information PeriodKout=Retained Information Period
11 LIRS (Low Inter-reference Recency Set) Maintains 2 LRU stacks of different size.Llirs maintains LRU page at least twice recently seen.Lhirs maintains LRU page only once recently seen.Works well for IRM, but not for SDD.
12 FBR (Frequency-Base Replacement) Divide LRU list into 3 sections;NewReference count in new section is not incremented.MiddleOldReplaces page in old section with smallest reference count.
13 LRFU (Least Recently/Frequently Used) Exponential smoothing.λ is hard to tune.
14 MQ (Multi-Queue) Uses m LRU queues Q0, Q1, … Qm-1 Qi contains page that have been seen [2i,2i+1) times recently.