ncm@zembu.com (Nathan Myers) writes:
> On Fri, Dec 01, 2000 at 09:13:28PM +1100, Philip Warner wrote:
>> You have raised some interesting issues regrading write-order etc. Can we
>> assume that when fsync *returns*, all records are written - though not
>> necessarily in the order that the IO's were executed?
> Not with ordinary disks. With a battery-backed disk server, yes.
I think the real point of this discussion is that there's no such thing
as an ironclad guarantee. That's why people make backups.
All we can do is the best we can ;-). In that light, I think it's
reasonable for Postgres to proceed on the assumption that fsync does
what it claims to do, ie, all blocks are written when it returns.
We can't realistically expect to persuade a disk controller that
reorders writes to stop doing so. We can, however, expect that we've
minimized the probability of failures induced by anything other than
disk hardware failure or power failure.
regards, tom lane