1. MemC3: Compact and Concurrent MemCache with Dumber Caching and Smarter Hashing

2. MemCache
Widely used for high-performance
Easy to use

3. MemCache
Interface
Get()

4. MemCache
Interface
Update()

5. MemCache Two parts: hash table & LRU lists Chaining
Variable k/v objects
Fixed 1MB page
Multi-chunks per page
Chunk size: 43 slab classes
Doubly-linked list for LRU

6. MemCache Threading Perf Enhance Originally single-threaded
Global lock 4 multi-threads
Perf Enhance
in-mem data to diff cores
Imbalanced loads

7. Problems with MemCache
Inspired by several K/V workloads
P1: small object
Keys < 32 bytes, values < 100~ bytes
56B header for each K/V object
Needs compact
P2: read heavy
Mutex locks, not optimized
P3: Low hash table occupancy ratio
Space efficiency -> more K/V objects

8. Goals of MemC3 Memory efficiency and throughput
High hash table occupancy ratio
Compact data structure
Concurrency: multi-reads/single-write

9. Re-designs
Hash table
Cache management

10. Cuckoo Hashing
Space efficiency
2 hashes
Example: A, H

11. Imprmt of Cuckoo 2 buckets, 4-way Tag 1-byte Tag-based lookup
Cache-friendly

12. Imprmt of Cuckoo 2 buckets, 4-way Tag 1-byte Tag-based insert
Cache-friendly
Never retrieve keys

13. Concurrent Cuckoo Obstacle1: w/w Obstacle2: r/w
deadlock risk
Sol: single write
Obstacle2: r/w
Floating victim key
Sol: execute backwards
Lookup/Insert lock two buckets(*)

14. MemC3’s Cache mgmt Problems Space overhead:
18 bytes, 2 pointers and 2-byte ref counters
Updates needs to be serialized
Sync bottleneck

15. MemC3’s Cache mgmt CLOCK replacement Approximate LRU update(): set 1
evict(): set 0 and forward until find 0
Question: map each bit to K/V object? 1 1 1
For each slab class 1 1

16. Performance