Re: Allowing WAL fsync to be done via O_SYNC

> Peter Eisentraut <peter_e@gmx.net> writes:
> > As a general rule, if something can be a run time option, as opposed to a
> > compile time option, then it should be.  At the very least you keep the
> > installation simple and allow for easier experimenting.
> 
> I've been mentally working through the code, and see only one reason why
> it might be necessary to go with a compile-time choice: suppose we see
> that none of O_DSYNC, O_SYNC, O_FSYNC, [others] are defined?  With the
> compile-time choice it's easy: #define USE_FSYNC_FOR_WAL, and sail on.
> If it's a GUC variable then we need a way to prevent the GUC option from
> becoming unset (which would disable the fsync() calls, leaving nothing
> to replace 'em).  Doable, perhaps, but seems kind of ugly ... any
> thoughts about that?

I don't think having something a run-time option is always a good idea. 
Giving people too many choices is often confusing.  

I think we should just check at compile time, and choose O_* if we have
it, and if not, use fsync().  No one will ever do the proper timing
tests to know which is better except us.  Also, it seems O_* should be
faster because you are fsync'ing the buffer you just wrote, so there is
no looking around for dirty buffers like fsync().

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