4a855c0799
Summary: sync_file_range is not always asyncronous and thus can block writes if we do this for WAL in the foreground thread. See more here: http://yoshinorimatsunobu.blogspot.com/2014/03/how-syncfilerange-really-works.html Some users don't want us to call sync_file_range on WALs. Some other do. Thus, I'm adding a separate option wal_bytes_per_sync to control calling sync_file_range on WAL files. bytes_per_sync will apply only to table files now. Test Plan: no more sync_file_range for WAL as evidenced by strace Reviewers: yhchiang, rven, sdong Reviewed By: sdong Subscribers: dhruba, leveldb Differential Revision: https://reviews.facebook.net/D38253