Abstract

B-trees are the data structure of choice for maintaining searchable data on disk. However, B-trees perform suboptimally • when keys are long or of variable length, • when keys are compressed, even when using front compression, the standard B-tree compression scheme, • for range queries, and • with respect to memory effects such as disk prefetching. This paper presents a cache-oblivious string B-tree (COSB-tree) data structure that is efficient in all these ways: • The COSB-tree searches asymptotically optimally and inserts and deletes nearly optimally. • It maintains an index whose size is proportional to the frontcompressed size of the dictionary. Furthermore, unlike standard front-compressed strings, keys can be decompressed in a memory-efficient manner. • It performs range queries with no extra disk seeks; in contrast, B-trees incur disk seeks when skipping from leaf block to leaf block. • It utilizes all levels of a memory hierarchy efficiently and makes good use of disk locality by using cache-oblivious layout strategies.

Citations