(Please bare with me, I'm a new, passionate, confident and terrified programmer :D ) Background: I'm pre-launch and 1 year into the development of my application. My target is to be able to eventually handle millions of registered users with 5-10% of them concurrent. Up to this point I've used auto-increment to assign unique identifiers to rows. I am now considering switching to a non-sequential strategy. Oh, I'm using the LAMP configuration. My reasons for avoiding auto-increment: 1. Complicates replication when scaling horizontally. Risk of collision is significant (when running multiple masters). Note: I've read the other entries in this forum that relate to ID generation and there have been some great suggestions -- including a strategy that uses auto-increment in a way that avoids this pitfall... That said, I'm still nervous about it. 2. Potential bottleneck when retrieving/assigning IDs -- IDs assigned at the database. My reasons for being nervous about non-sequential IDs: 1. To guarantee uniqueness, the IDs are going to be much larger -- potentially affecting performance significantly My New Strategy: (I haven't started to implement this... I'm waiting for someone smarter than me to steer me in the right direction) 1. Generate a guaranteed-unique ID by concatenating the user id (1-9 digits) and the UNIX timestamp(10 digits). 2. Convert the resulting 11-19 digit number to base_36. The resulting string will be alphanumeric and 6-10 characters long. This is, of course, much shorter (at least with regard to characters) then the standard GUID hash. 3. Pass the new identifier to a column in the database that is type CHAR() set to binary. My Questions: 1. Is this a valid strategy? Is my logic sound or flawed? Should I go back to being a graphic designer? 2. What is the potential hit to performance? 3. Is a 11-19 digit number (base 10) actually any larger (in terms of bytes) than its base-36 equivalent? I appreciate your insights... and High Scalability for supplying this resource!