On Wed, Nov 17, 2004 at 10:32:48PM +0000, Simon Riggs wrote: > The main issue is that PostgreSQL's default histogram statistics setting > is lower than other RDBMS. This means that it is less able to > discriminate between cases such as yours that are close to the edge. > This is a trade-off between run-time of the ANALYZE command and the > benefit it produces. As Joshua suggests, increasing the statistics > target for this table will likely allow the optimizer to correctly > determine the selectivity of the index and take the right path. Is there still a good reason to have the histogram stats so low? Should the default be changed to more like 100 at this point? Also, how extensively does the planner use n_distinct, null_frac, reltuples and the histogram to see what the odds are of finding a unique value or a low number of values? I've seen cases where it seems the planer doesn't think it'll be getting a unique value or a small set of values even though stats indicates that it should be. One final question... would there be interest in a process that would dynamically update the histogram settings for tables based on how distinct/unique each field was? -- Jim C. Nasby, Database Consultant decibel@xxxxxxxxxxx Give your computer some brain candy! www.distributed.net Team #1828 Windows: "Where do you want to go today?" Linux: "Where do you want to go tomorrow?" FreeBSD: "Are you guys coming, or what?"
