Il giorno 29 gen, 2010 9:20 m., "Joe Kramer" <cckramer@gmail.com> ha scritto:
Hello,
I need to generate unique id which is not guessable unlike serial(integer) type. I need an id in format like md5 hash of random number. On top of that I need this id to be unique across multiple tables.
Anyone had to solve this problem before? Can you post any recipes or best practices please?
My questions:
1. Avoiding collisions. If I make an UNIQUE constraint and do generation of id triggered on INSERT. What if collision happens? DO I nee d to check if unique hash already exists and if not- regenerate. This looks too primitive. Is there a readily available function or methodology to do that?
2. Generating global unique id across multiple tables. How to do that? My only idea is to have separate table to keep all hashes and compare for collision against that table. Is there a better way? Maybe by creating some special serial type that is not integer but varchar?
3. what function to use to generate 64-bit random hash without much overhead to CPU?