The vagabond approach to logging and recovery in transaction-time temporal object database systems

In most current database systems, data is updated in-place. In order to support recovery and increase performance, write-ahead logging is used. This logging defers the in-place updates. However, sooner or later, the updates have to be applied to the database. Even if this is done as a batch operation, it can result in many nonsequential writes. In order to avoid this, another approach is to eliminate the database completely and use a log-only approach. In this case, the log is written contiguously to the disk, in a no-overwrite way using large blocks. When using the log-only approach keeping previous versions comes almost for free, and this approach is therefore particularly interesting for transaction-time temporal object database systems. Although the log-only approach in its basic form is relatively straightforward, it is not trivial to support features such as steal/no-force buffer management, fuzzy checkpointing, and fast commit. We describe, in detail, algorithms and strategies for object and log management that make support for these features possible.