The Persistent Cache: Improving OID Indexing in Temporal Object-Oriented Database Systems

In a temporal OODB, an OID index (OIDX) is needed to map from OID to the physical location of the object. In a transaction time temporal OODB, the OIDX should also index the object versions. In this case, the index entries, which we call object descriptors (OD), also include the commit timestamp of the transaction that created the object version. The OIDX in a non-temporal OODB only needs to be updated when an object is created, but in a temporal OODB, the OIDX has to be updated every time an object is updated. This has previously been shown to be a potential bottleneck, and in this paper, we present the Persistent Cache (PCache), a novel approach which reduces the index update and lookup costs in temporal OODBs. We develop a cost model for the PCache, and use this to show that the use of a PCache can reduce the average access cost to only a fraction of the cost when not using the PCache. Even though the primary context of this paper is OID indexing in a temporal OODB, the PCache can also be applied to general secondary indexing, and can be especially beneficial for applications where updates are non-clustered.