[kentonv]

Weird take?

It is a table stakes expectation for most servers that they will not lose data when the power goes out, or when the kernel panics, or when the server itself crashes or runs out of memory. If your software requires graceful shutdown, that seems to imply that it will lose data in all those cases.

You can perhaps use graceful shutdown to perform some optimization that allows subsequent startup to go faster, e.g. put things in a clean state that avoids the need for a recovery pass on the next startup... but these days with good journaling techniques "recovery" is generally very fast. When that's the case, it's arguably better to always perform non-graceful shutdown to make sure you are actually testing your recovery code, otherwise it might turn out not to work when you need it.

So yeah, I agree with SoftTalker. Assume all shutdowns will be sudden and unexpected, and design your code to cope with that.

[empthought]

That software should not “even expect” a graceful shutdown is the weird take.

Servers can and do “lose data” all the time when they’re shut down unexpectedly. I don’t know why you’d think they don’t. If the data has been read from somewhere (a socket maybe) and not fsynced, it’ll be lost. I agree that the system needs to be designed in such a way that this is a recoverable state, but I disagree with the ideas that applications should not have a mode where buffers can accumulate for some period of time without being fsynced, and that there should be no attention paid to the common case, which is planned process stops (aka SIGTERMs) for a variety of reasons. System shutdown just being one of those reasons.

[kentonv]

By "lose data" I mean losing a confirmed write. That is, the server got a request to modify some state, and it responded to the request indicating success, but the change is later lost. Generally it's expected that databases will not lose confirmed writes, unless the application has explicitly made the decision that this is acceptable and opted into possible data loss to improve performance.

[lmz]

I think in that situation they expect you to not ack the data before you called fsync (which is the same expectation most people have of their SQL database). Then the remote end can retry the operation.