Buffering Accesses to Memory-Resident Index Structures

摘要

Recent studies have shown that cache-conscious indexes outperform conventional main memory indexes. Cache-conscious indexes focus on better utilization of each cache line for improving search performance of a single lookup. None has exploited cache spatial and temporal locality between consecutive lookups. We show that conventional indexes, even "cache-conscious" ones, suffer from significant cache thrashing between accesses. Such thrashing can impact the performance of applications such as stream processing and query operations such as index-nested-loops join. We propose techniques to buffer accesses to memory-resident tree-structured indexes to avoid cache thrashing. We study several alternative designs of the buffering technique, including whether to use fixed-size or variable-sized buffers, whether to buffer at each tree level or only at some of the levels, how to support bulk access while there are concurrent updates happening to the index, and how to preserve the order of the incoming lookups in the output results. Our methods improve cache performance for both cache-conscious and conventional index structures. Our experiments show that buffering techniques enable a probe throughput that is two to three times higher than traditional methods.