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We report the results of a study to compare the performance of two commondatabase indexing methods, HTM and HEALPix, on Solaris and Windows databaseservers installed with PostgreSQL, and a Windows Server installed with MS SQLServer. The indexing was applied to the 2MASS All-Sky Catalog and to the HubbleSource Catalog, which approximate the diversity of catalogs common inastronomy. On each server, the study compared indexing performance bysubmitting 1 million queries at each index level with random sky positions andrandom cone search radius, which was computed on a logarithmic scale between 1arcsec and 1 degree, and measuring the time to complete the query and write theoutput. These simulated queries, intended to model realistic use patterns, wererun in a uniform way on many combinations of indexing method and indexingdepth. The query times in all simulations are strongly I/O-bound and are linearwith number of records returned for large numbers of sources. There are,however, considerable differences between simulations, which reveal thathardware I/O throughput is a more important factor in managing the performanceof a DBMS than the choice of indexing scheme. The choice of index itself isrelatively unimportant: for comparable index levels, the performance isconsistent within the scatter of the timings. At small index levels (largecells; e.g. level 4; cell size 3.7 deg), there is large scatter in the timingsbecause of wide variations in the number of sources found in the cells. Atlarger index levels, performance improves and scatter decreases, but theimprovement at level 8 (14 arcmin) and higher is masked to some extent in thetiming scatter caused by the range of query sizes. At very high levels (20;0.0004 arsec), the granularity of the cells becomes so high that a large numberof extraneous empty cells begin to degrade performance.

A Study of the Efficiency of Spatial Indexing Methods Applied to Large Astronomical Databases