问题
I have three main constraints for int8 key generation:
- Keys need be unpredictably random
- Number of rows created should not be calculable
- Order of row creation should not be calculable
- Keys need to be unique across the entire db
- Future table merges should not require changing keys
- Future Table-Per-Class superclass additions should not require changing keys
- Keys need to be bounded
- These keys will be base58 encoded in various places such as URLs
- Range will be narrower at first but should be adjustable in future to meet demand
I have heard of a few approaches to tackling at least some of these constraints:
DB-wide serial8
Does not meet the first constraint, but meets the second and third constraints.
DB-wide serial8 combined with a cipher
If the cipher key is leaked or discovered at any point then this becomes just DB-wide serial8, since the cipher key can't be changed without changing all the existing keys.
UUIDs
Does not meet the last constraint due to their 128-bit nature, but meets the first and second constraints.
Set default to floor(random() * n)
Does not meet the second constraint due to collision risk, but meets the first and last constraints.
Using random combined with a keys base table to keep track of all the keys
This does sort of meet all the constraints. However if a duplicate key is generated the insertion will fail. I am also concerned about any performance / locking issues.
If there is a nice way to make this re-roll until a non-colliding key is found, with good performance, then this would be an acceptable solution.
What is the best way to generate keys in PostgreSQL that meets the three criteria I listed?
回答1:
If you expect to have no more than a billion identifiers, then generating random 64-bit numbers (so 2^64 possible values) may suit your purposes, as long as you have a way to check those numbers for uniqueness. They should be generated using a cryptographic random number generator (such as secrets.SystemRandom in Python or random_int in PHP).
With random numbers this long, the expected chance of producing a duplicate will be less than 50% after generating a billion random numbers (see "Birthday problem" for more precise formulas).
来源：https://stackoverflow.com/questions/59410237/key-generation-that-is-random-unique-db-wide-and-bounded