Good hash functions almost never have 'collisions' as they are called, duplicates, as long as you stay under a certain percentage of the bits for the number of entries.
Read up on WikiPedia, but I believe that no Hash Function is much good above 50% of the address space it generates. Many are much worse. Some are exceptional. Just know what you are using. Cosmic rays are not much of a problem at sea level . . . but that changes linearly with altitude. The astronauts regulary see micro flashes in there vision . . as cosmic rays go through their retina or optical nerves. Dennis Gearon Signature Warning ---------------- It is always a good idea to learn from your own mistakes. It is usually a better idea to learn from others’ mistakes, so you do not have to make them yourself. from 'http://blogs.techrepublic.com.com/security/?p=4501&tag=nl.e036' EARTH has a Right To Life, otherwise we all die. ----- Original Message ---- From: Yonik Seeley <yo...@lucidimagination.com> To: solr-user@lucene.apache.org Sent: Tue, November 16, 2010 1:46:43 PM Subject: Re: hash uniqueKey generation? On Tue, Nov 16, 2010 at 5:31 AM, Dennis Gearon <gear...@sbcglobal.net> wrote: > hashing is not 100% guaranteed to produce unique values. But if you go to enough bits with a good hash function, you can get the odds lower than the odds of something else changing the value like cosmic rays flipping a bit on you. -Yonik http://www.lucidimagination.com
