Abstract:

 Kurzweil says, computers will enable people to live forever and doctors 
 will be doing backup of your memories by late 2030. This talk is not 
 about that, yet.
 Instead, the remarkable drop in disk costs makes it possible and 
 attractive to retain past application states and store them for a long 
 time for mining or auditing.
 A still open question is how to best organize the past state storage?
 Split snapshots are a recent approach to past state storage that is 
 attractive for several reasons. Split snapshots are persistent, can be 
 taken with high-frequency, and they are transactionally consistent. 
 Unmodified database code can run against them.
 Like no other past state storage approach, they provide low-cost 
 discriminated garbage collection of snapshots, a useful capability in 
 long-lived systems since since indiscriminately keeping all snapshots 
 accessible becomes impractical over time even if raw disk storage is cheap,
 because administering such large-volume storage is expansive over long 
 duration.

 A number of novel techniques underly split snapshots.
 A new in-memory data-structure creates consistent copy-on-write snapshots 
 without blocking, a new persistent data structure provides high 
 performance versioned meta-data, and a new snapshot storage organization 
 allows to gradually garbage collect selected copy-on-write snapshots without 
 creating disk-fragmentation and without copying.
 Measurements of a split snapshot prototype system indicate that the new 
 techniques are efficient and scalable, imposing minimal ($4\%$) performance 
 penalty on a storage system, on expected common workloads.
 

 Bio:
 Liuba Shrira is a Professor of Computer Science at Brandeis University and
 doubles as Research Affiliate at MIT/CSAIL.
 She received her B.Sc./M.Sc./D.Sc. from Computer Science Department at 
 Technion, what seems like yeasterday,
 and is always delighted to visit her Alma Mater.