Hig igh-Performance Key- Carnegie Mellon Value Store University - PowerPoint PPT Presentation

Hyeontaek Lim , Bin Fan, SIL ILT: A Memory ry-Efficient, David G. Andersen Michael Kaminsky† Hig igh-Performance Key- Carnegie Mellon Value Store University †Intel Labs Presented by: Ramya Danappa

Seesaw Game? FAWN-DS How can we FlashStore improve? HashCache SkimpyStash BufferHash Memory efficiency High performance 2

(1) “The memory overhead and lookup performance of SILT and the recent key - value stores. For both axes, smaller is better.” Exp Explain the the po positions of of FAWN-DS, S, Ski SkimpyStash, , Bu BufferHash, and and SIL SILT T on on the the grap aph. Read amplification 6 SkimpyStash HashCache 4 BufferHash FlashStore 2 FAWN-DS SILT 0 0 2 4 6 8 10 12 Memory overhead (bytes/entry) 3

Describe SILT’s structure (Architecture of SILT). Compared with LevelD lDB, SIL ILT T has has onl only thr three levels. What’s concern with a multi -le level KV KV stor ore whe hen it it ha has too oo few le levels?

“SILT uses a memory ry-effi ficient, hig igh-performance hash sh table le base sed upon cuckoo hashing.”. Explain what the cuckoo hash shin ing is is and why y it it is is use sed. R. Pagh and F. Rodler. Cuckoo hashing. Journal of Algorithms, (2): 122 – 144, May 2004.

Desig ign of f LogStore: an in in-memory cu cuckoo hash table (in (index and fil filter) to describe how a PUT request and a GET request is is served in in a LogStore. In In particular, explain how th the tag is is used in in a LogStore for cu cuckoo hashing

Explain how a LogStore is converted into a HashStore?

“Once a LogStore fills lls up up (e (e.g., the insertio ion alg lgorithm terminates without finding any vacant slo lot after a maxim imum number of of dis ispla lacements ts in in the hash table), SILT freezes the LogStore and converts ts it it into a more memory ry-efficie ient data str tructure. ” Compared to to LogStore, what’s th the advantage of of HashStore? Why doesn’t SILT create HashStore at at the beg beginnin ing (w (wit ithout fi first cr creating Log LogStore)? )? Advantage of Hashstore over logstore: • Hashstore saves memory over Logstore by eliminating the index and reordering the on-flash (key,value) pairs from insertion to hash order. SILT create Logstore first because so every data ideally should store on flash.

“When fixed -le length key-valu lue en entrie ies ar are sort orted by y key on on fl flash ash, a a tri trie for or the the sho hortest uni unique pr prefix fixes of of the the keys ser erves as as an an index for these sorted data.” While a So Sort rtedStor ore is ful fully ly sort orted, cou ould ld you ou comment on on the the cos ost of of me mergi ging g a a Has HashStor ore wi with th a a So Sort rtedStor ore? Co Comp mpare thi this cos ost to o the the ma majo jor com ompaction on cos ost for or Le LevelDB? • Cost is proportional to the size of Database. • SILT is worse because single sorted store leads to bad write amplification.

Questions?

Thank you