Summary:
the return value for `ErrorHandler::SetBGError(error)` seems to be not well-defined, it can be `bg_error_` (no matter if the `bg_error_` is set to the input error), ok status or [`recovery_error_`](3ee4d5a11a/db/error_handler.cc (L669)) from `StartRecoverFromRetryableBGIOError()`. The `recovery_error_` returned may be an OK status.
We have only a few places that use the return value of `SetBGError()` and they don't need to do so. Using the return value may even be wrong for example in 3ee4d5a11a/db/db_impl/db_impl_write.cc (L2365) where a non-ok `s` could be overwritten to OK. This PR changes SetBGError() to return void and clean up relevant code.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/12792
Test Plan: existing unit tests and go over all places where return value of `SetBGError()` is used.
Reviewed By: hx235
Differential Revision: D58904898
Pulled By: cbi42
fbshipit-source-id: d58a20ba5a40e3f35367c6034a32c755088c3653
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