Lazy Reference Counting for Transactional Storage Systems Miguel Castro, Atul Adya, Barbara Liskov Lab oratory for Computer Science, Massachusetts Institute of Technology, 545 Technology Square, Cambridge, MA 02139 fcastro,adya,
[email protected] Abstract ing indirection table entries in an indirect pointer swizzling scheme. Hac isanovel technique for managing the client cache Pointer swizzling [11 ] is a well-established tech- in a distributed, p ersistent ob ject storage system. In a companion pap er, we showed that it outp erforms nique to sp eed up p ointer traversals in ob ject- other techniques across a wide range of cache sizes oriented databases. For ob jects in the client cache, and workloads. This rep ort describ es Hac's solution it replaces contained global ob ject names by vir- to a sp eci c problem: how to discard indirection table tual memory p ointers, therebyavoiding the need to entries in an indirect pointer swizzling scheme. Hac uses translate the ob ject name to a p ointer every time a lazy reference counting to solve this problem. Instead reference is used. Pointer swizzling schemes can b e of eagerly up dating reference counts when ob jects are classi ed as direct [13 ] or indirect [11 , 10 ]. In direct mo di ed and eagerly freeing unreferenced entries, which schemes, swizzled p ointers p oint directly to an ob- can b e exp ensive, we p erform these op erations lazily in the background while waiting for replies to fetch and ject, whereas in indirect schemes swizzled p ointers commit requests. Furthermore, weintro duce a number p oint to an indirection table entry that contains of additionaloptimizations to reduce the space and time a p ointer to the ob ject.