shared token selector: subscribe to the token DB write operations

[adecaro]

We can subscribe to the token DB write operations and populate the token cache whenever a new token is added/deleted.

[atharrva01]

Hi @adecaro, I'd like to take this one.

I worked on the sherdlock selector metrics in PR #1459, so I'm familiar with the cachedFetcher in token/services/selector/sherdlock/fetcher.go. Currently the cache is refreshed on a time-based interval (freshnessInterval) or after maxQueriesBeforeRefresh queries, which means there's always a staleness window between a token being written/deleted in the DB and the cache reflecting that change.

I can see that driver.TokenNotifier already exists in token/services/storage/db/driver/token.go with a Subscribe(callback func(Operation, TokenRecordReference)) error method, and there are already integration test cases for it in token/services/storage/db/dbtest/tokensnotifier.go. The infrastructure is in place, the missing piece is wiring a subscription into cachedFetcher so the cache is invalidated (and optionally refreshed) eagerly on INSERT/DELETE operations rather than only on the next poll tick.

My plan: subscribe to TokenNotifier during cachedFetcher initialization, and on each callback, invalidate the relevant cache key so the next fetch is forced to go to the DB. This eliminates the staleness window for the common case without removing the periodic refresh as a safety net.

Could you assign this to me?

[adecaro]

Hi @atharrva01 , thanks for offering your time on this. Please, go ahead 🙏