What should primary keys be?
The Proposed Server API page asks "What do we want keys to be?".
This page collects and evaluates the options.
User-allocated variable-length or long fixed-length keys
- These longer keys must be passed around in requests.
- The master needs a hash table.
- There is some feature overlap with indexes. Now you need an extremely fast "primary index" on the master to look up objects.
User-allocated 64-bit keys
- I think there's a consensus that this is not a large enough space to be used as a reasonable hash value, so the only real use case is ICQ.
System-allocated 64-bit keys with reuse
- This is by far the easiest solution to implement. Bertha's (multi-level indexes analogous to page tables) seem to be the data structure of choice.
- Dangling pointers in the application are extremely dangerous. If your application gets back the same type of object as was originally identified by that key, it will not crash but rather it is likely to leak information.