Statement cache should be aware of errors

[Martin2112]

If one of the statements obtained from the cache in mysql/tree_storage.go errors the cache should be instructed to either drop it or clear all the prepared statements. At the moment there are some situations that are not recoverable (database server restart).

[Martin2112]

Another option is to just remove the statement cache and measure performance. None of our queries should need complex parsing except subtree fetching.

[codingllama]

+1 for removing the statement cache (after measuring impact). I suspect it's mostly unneeded complexity.

[Martin2112]

Putting this in M7 provisionally as we should find out early if there are any performance issues.

[Martin2112]

Closing this for the moment as we have no plans to implement it and the current code works.

[yryz]

We ran into this issue in production, can we reopen it?
https://groups.google.com/a/chromium.org/g/ct-policy/c/r1QXGbWDRes