https://bugs.openldap.org/show_bug.cgi?id=10066
--- Comment #3 from Howard Chu hyc@openldap.org --- Yes, the perf cost is extreme. We found the same in our own testing.
Is it indeed true what people say: that most drives lie about fsync anyway, that this stuff doesn't matter that much, and that people mostly just prefer the speed?
Yes, most drives lie, and most people prefer the speed.
The need for a safe sync seems to be greatest on Windows, because the OS itself is prone to crashing, which makes ensuring that OS buffers get persisted to disk a higher priority. True hardware failures will hit all OSs equally but they're quite rare as it is. Another point in Apple's favor is that most of their devices these days are mobile, with built in batteries, so OS crashes due to sudden power outages are pretty unheard of too.
On my own Linux laptops I usually run with all fsyncs disabled, and the OS cache writeback set to 10 minutes. There's just no need for frequent flushing; the most common failure is application-level crashes, which have zero impact on LMDB as it is.