Bad assertion in DBImpl::MarkLogsSynced()

[bdbyrne]

I'm hitting the following assertion in DBImpl::MarkLogsSynced():
assert(logs_.empty() || (logs_.size() == 1 && !logs_[0].getting_synced));

This appears to be due to a DBImpl::SyncWAL() call that sets exactly 0 logs to getting_synced = true, because the loop breaks immediately from condition it->number <= current_log_number failing. The mutex is unlocked, during which time another DBImpl::SyncWAL() is called that marks the first entry with getting_synced = true. The first call reacquires the mutex, then enters DBImple::MarkLogSynced(), tripping on the assertion.

I would appreciate someone verifying the scenario is valid and performing the appropriate fix.

[siying]

Let me take a look.

[siying]

@bdbyrne other than SyncWAL(), do you do normal sync writes?

[siying]

I don't quite understand what you described, but I can repro the assert failure by having SyncWAL() run concurrently with log rolling: https://reviews.facebook.net/D54621

Is there a way you can verify whether it is the problem you ran into?

[bdbyrne]

Yes, normal sync writes are used quite heavily in my environment, where various updates are required to be persistent before being acknowledged.

Your fix is similar to mine, so I can say it resolves my issue. Thanks for investigating, @siying.

[gfosco]

Closing this via automation due to lack of activity. If discussion is still needed here, please re-open or create a new/updated issue.