,
Sebastian Wild
Creative Commons Attribution 4.0 International license
Lazy search trees (Sandlund & Wild FOCS 2020, Sandlund & Zhang SODA 2022) are sorted dictionaries whose update and query performance smoothly interpolates between that of efficient priority queues and binary search trees - automatically, depending on actual use; no adjustments are necessary to the data structure to realize the cost savings. In this paper, we design lazy B-trees, a variant of lazy search trees suitable for external memory that generalizes the speedup of B-trees over binary search trees wrt. input/output operations to the same smooth interpolation regime. A key technical difficulty to overcome is the lack of a (fully satisfactory) external variant of biased search trees, on which lazy search trees crucially rely. We give a construction for a subset of performance guarantees sufficient to realize external-memory lazy search trees, which we deem of independent interest. As one special case, lazy B-trees can be used as an external-memory priority queue, in which case they are competitive with some tailor-made heaps; indeed, they offer faster decrease-key and insert operations than known data structures.
@InProceedings{rysgaard_et_al:LIPIcs.MFCS.2025.87,
author = {Rysgaard, Casper Moldrup and Wild, Sebastian},
title = {{Lazy B-Trees}},
booktitle = {50th International Symposium on Mathematical Foundations of Computer Science (MFCS 2025)},
pages = {87:1--87:19},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-388-1},
ISSN = {1868-8969},
year = {2025},
volume = {345},
editor = {Gawrychowski, Pawe{\l} and Mazowiecki, Filip and Skrzypczak, Micha{\l}},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.MFCS.2025.87},
URN = {urn:nbn:de:0030-drops-241949},
doi = {10.4230/LIPIcs.MFCS.2025.87},
annote = {Keywords: B-tree, lazy search trees, lazy updates, external memory, deferred data structures, database cracking}
}