TBS: "Value log GC request rejected" error

[carsonip]

Errors observed in the wild: message "tail sampler aborted" with error.message "Value log GC request rejected".

Due to #14337 , it is possible to have 2 TBS GC goroutine running concurrently, which will cause one of them to crash. In a hot reload under EA, if the new server's GC crashed, and the old server's GC later stopped as part of the reload, this will leave the server with no GC and the TBS storage size will keep growing.

APM Server version (apm-server version): observed on 8.14.3