Lazy timestamping in transaction time database

摘要

Lazy timestamping in a transaction time database is performed using volatile reference counting and checkpointing. Volatile reference counting is employed to provide a low cost way of garbage collecting persistent timestamp information about a transaction by identifying exactly when all record versions of a transaction are timestamped and the versions are persistent. A volatile timestamp (VTS) table is created in a volatile memory, and stores timestamp, reference count, transaction ID, and LSN information. Active portions of a persisted timestamp (PTS) table are stored in the VTS table to provide faster and more efficient timestamp processing via accesses to the VTS table information. The reference count information is stored only in the VTS table for faster access. When the reference count information decrements to zero, it is known that all record versions that were updates for a transaction were timestamped. A checkpointing component facilitates checkpoint processing for verifying that timestamped records have been written to the persistent database and that garbage collection of the PTS table can be performed for transaction entries with zero reference counts.