María Fabiana Piccoli

Very Fast All k-Nearest Neighbors in Metric and Non Metric Spaces without Indexing

Proximity queries consists in retrieving objects near a given query. To avoid a brute force scan over a large database, an index can be used. However, for some problems, indexes are mostly useless their running times are worst than sequential scan. On the other hand, researchers have tried massively parallel hardware as GPGPU in the quest of faster query times. The results have been modest because current algorithms are cumbersome, while GPGPU architectures favor simple kernels, have a clear memory hierarchy and need close to zero cross-talk between processing units. We have engineered very fast algorithms for proximity queries taking into account this principles, all of them are presented in this paper. In our approach no index is built, the cross-talk between threads is eliminated, and the higher faster levels of memory hierarchy are consistently used. The absence of data structures allows to use all the available memory for the database, and furthermore makes possible to do stream processing on very large data collections.