man nfs

man nfs

Posted Mar 5, 2020 22:07 UTC (Thu) by NYKevin (subscriber, #129325)
In reply to: man nfs by flussence
Parent article: Quote of the week

IMHO this is a problem with the entire space of filesystems that purport to comply with POSIX. NFS is particularly bad because it has a long history of failing to adequately comply with POSIX, but in general, the POSIX filesystem API seems to be a "worst of all possible worlds" situation:

• Filesystem developers heavily optimize the "no fsyncs ever" case, because POSIX offers no guarantees in that case. When people ask for a richer API, their usual reaction is somewhere between "just call fsync" and "why would you want that?"
• Database developers call fsync religiously, because POSIX offers no guarantees if you don't. Then they complain about performance and resort to nasty hacks like O_DIRECT, which tends to annoy the FS developers.
• (Some) application developers blithely ignore all of this and just assume their data will be fine. They don't call fsync or necessarily even know that it exists. They might stuff their data into an SQLite database (or a "real" database) which does it for them. The prudent ones also do periodic autosaving, and recover the last usable save if the latest data on disk is bad. Occasionally, the filesystem developers will manage to break someone's autosaving system (which was never guaranteed to work in the first place), and then Bad Things happen and people yell at each other.
• End users are usually in a position of even greater ignorance than the application developers. Inevitably, some of their data will get lost, since it's completely impossible to avoid losing any data whatsoever without slowing performance to a crawl. No matter what data gets lost, some users will be unhappy.

This process inevitably leads to O_PONIES conflicts and people talking past each other about what they actually want. It is unpleasant to watch from my vantage point on the sidelines; I can't imagine how immensely frustrating it must be to actually participate in these Sisyphean discussions.

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