如何通过部署在没有数据库的多个服务器上的服务为每个呼叫生成一个 16 位唯一号码？

Question

I have a Java service that generates a 16 digit unique number using current time in the format yymmddhhmmssmsms. And it handles multiple calls on the same mili-second using Atomic Long. But now the problem is that I need this service on multiple cloud machines. How can I handle calls at the same microsecond on different servers and generate a unique number for each of this calls. And I dont want to use database for this.

EDIT: I understand UUID can be a solution. But UUID generates a random no. everytime, not unique, though the chances of collision are very low.

Answer 1

A think, you can try to use UUID.randomUUID() object

Answer 2

The UUID v4 is the right choice for distributed systems.

The UUID v4 implementation uses random numbers as the source. The Java implementation is SecureRandom – which uses an unpredictable value as the seed to generate random numbers to reduce the chance of collisions. Source: https://www.baeldung.com/java-uuid

Secure Random: This class provides a cryptographically strong random number generator (RNG). Source: https://docs.oracle.com/javase/8/docs/api/java/security/SecureRandom.html

Example how to use the UUID:

UUID uuid = UUID.randomUUID();

Answer 3

Using a random number alone (such as a random UUID) should only be done if—

• you have a way to check the number for uniqueness across all calls, or
• you can tolerate the risk of generating the same number for different calls.

If you find it appropriate, try assigning each server a unique number (eg, by requesting a unique number from a central database). Then each server can generate a unique ID for each call it makes by appending a random number to that unique number; this may work well because the server can now more easily check the IDs it then generates for uniqueness, as no further contact with a central database or other servers is required.

See also my section on generating unique random identifiers .