Kerttu Pollari Malmi, Eljas Soisalon-Soininen, Jarmo Ruuth:

Concurrency Control for B-Trees with Differential Indices

Abstract:

We present an indexing system where a database index is divided into
two parts: the main index located on disk and the differential
index in the main memory. Both indices are implemented
as B-trees. All updates performed by active
transactions are written in the differential index. Periodically,
writes of committed transactions are transferred from differential
index to the main index as a batch-update operation. Thus, updates
falling into the same leaf of the tree can be performed simultaneously.
In addition, the system offers a simple recovering scheme. After a system
crash, no undo operations are needed and redo operations need only
write to the main memory.