This is what I'm considering for "fsync always", but for "fsync everysec" this is now ideal unfortunately. Still O_SYNC can be able to fix at least one problem,

This is what I'm considering for "fsync always", but for "fsync everysec" this is now ideal unfortunately. Still O_SYNC can be able to fix at least one problem, that's cool :) Thanks for the comment. Edit: worth noting that instead O_DIRECT can't be used for an append only file, because of alignment requirements. Edit 2: yep O_SYNC helps a lot. Just updated the post with the results.