[EMAIL PROTECTED] wrote:
Something to think about:
if you run PostgreSQL with fsync on, but you use the hardware write cache on your disk drives, how likely are you to lose data? Obviously, this is a fairly limited problem, as it only applies to power down (which you can control) or power loss where the risks may be reduced but not eliminated with a UPS.
Does it make sense to add a platform specific call that will flush a write cache when fsync is enable?
Pete Zaitsev from mysql wrote that there is a special call on Mac OS: Quoting him:
Mac OS X also has this "optimization", but at least it provides an alternative flush method for Database Servers:
fcntl(fd, F_FULLFSYNC, NULL)
can be used instead of fsync() to get true fsync() behavior.
I couldn't confirm this with a quick google search - perhaps someone with MacOS docs (or mysql sources) should check it.
What might be useful is a test tool that benchmarks fsync: if it's faster than the rotational speed of a 15k rpm disk then probably someone caches the write calls.
-- Manfred
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