Jim C. Nasby wrote: > > Index scans are also pretty picky about correlation. If you have really > low correlation you don't want to index scan, I'm still don't think "correlation" is the right metric at all for making this decision. If you have a list of addresses clustered by "zip" the "correlation" of State, City, County, etc will all be zero (since the zip codes don't match the alphabetical order of state or city names) but index scans are still big wins because the data for any given state or city will be packed on the same few pages - and in fact the pages could be read mostly sequentially. > but I think our current > estimates make it too eager to switch to a seqscan.
