Not the OP but perhaps if only accounting cared about it you could assign these IDs separately as some asynchronous single threaded process. This would only wor

Not the OP but perhaps if only accounting cared about it you could assign these IDs separately as some asynchronous single threaded process. This would only work if insert rates were low enough or the assignment of the gapless sequence only needed to be eventually concistent over some window of time (i.e. before next payroll we must have assigned gapless IDs to all the new user accounts)