Lazy and Speculative Execution

15 January 2007

Lampson: Lazy and Speculative Execution

Lazy: Copy-on-Write (CoW)

nKeep multiple versions of a slowly changing state

oBe lazy about allocating space for a new version

▬Do it only when there’s new data in either version

▬Otherwise, share the old data

oUsually in a database or file system

nThe bet: Data won’t be overwritten.

oUsually an easy win.

nBig win in latency when making a new version

nBig win in bandwidth if versions differ little

nRep: Data shared among versions (need GC)