> > I see that seek+write was changed to write-s in XLogFileInit
> > (that was induced by subj, right?), but what about problem
> > itself?
>
> > BTW, were performance tests run after seek+write --> write-s
> > change?
>
> That change was for safety, not for performance. It might be a
> performance win on systems that support fdatasync properly (because it
> lets us use fdatasync), otherwise it's probably not a performance win.
Even with true fdatasync it's not obviously good for performance - it takes
too long time to write 16Mb files and fills OS buffer cache with trash-:(
Probably, we need in separate process like LGWR (log writer) in Oracle.
I also like the Andreas idea about re-using log files.
> But we need it regardless --- if you didn't want a fully-allocated WAL
> file, why'd you bother with the original seek-and-write-1-byte code?
I considered this mostly as hint for OS about how log file should be
allocated (to decrease fragmentation). Not sure how OSes use such hints
but seek+write costs nothing.
Vadim