Cabin: A Compressed Adaptive Binned Scan Index

Abstract

Scan is a fundamental operation widely used in main-memory analytical database systems. To accelerate scans, previous studies build either record-order or sort-order structures known as scan indices. While achieving good performance, scan indices often incur significant space overhead, limiting their use in main-memory databases. For example, the most recent and best performing scan index, BinDex, consists of a sort-order position array, which is an array of rowIDs in the value order, and a set of record-order bit vectors, representing records in pre-defined value intervals. The structures can be much larger than the base data column size. In this paper, we propose a novel scan index, Cabin, that exploits the following three techniques for better time-space tradeoff. 1) filter sketches that represent every 2^w-2 value intervals with a w-bit sketched vector, thereby exponentially reducing the space for the bit vectors; 2) selective position array that removes the rowID array for a fraction of intervals in order to lower the space overhead for the position array; and 3) data-aware intervals that judiciously select interval boundaries based on the data characteristics to better support popular values in skewed data distributions or categorical attributes. Experimental results show that compared with state-of-the-art scan solutions, Cabin achieves better time-space tradeoff, and attains 1.70 -- 4.48x improvement for average scan performance given the same space budget.