* Alerting: Prevent short uid collision in legacy migration when db is case-insensitive
Two factors come into play that cause sporadic uid conflicts during legacy alert migration:
- MySQL and MySQL-compatible backends use case-insensitive collation.
- Our short uid generator is not a uniform RNG and generates uids in such a way that generations in quick succession have a higher probability of creating similar uids.
Normally we would be guaranteed unique short uid generation, however if the source alphabet contains
duplicate characters (for example, if we use case-insensitive comparison) this guarantee is void.
Generating even ~1000 uids in quick succession is nearly guaranteed to create a case-insensitive
duplicate.
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