On Tue, May 22, 2012 at 06:59:25PM -0700, Wolfgang S. Rupprecht wrote:
> The first sync was to queue up the blocks to be written. That sync(1)
> call would not block. The second call would block until the flush
> finished. The third one was just for luck. Or something.
"Just to be sure."
Sync under Unix used to be systemwide--dunno if that was changed later, or
is different in Linux. But it caused some major headaches--essentially,
any user could cause the system to stop what it was doing and sync.
Not too bad if there are only a few users.
Very bad if there are, say, 300 users.
Back around 1983 or so, I was on contract at at Bell Labs working on the
5ESS Field Test Set. (This was the first portable Unix system--an 8086
with a custom MMU running System III in a box that _just_ fit under
an airline seat; weighed about 40 pounds. Booted from a floppy--my
work, that. I walked in one day with a floppy drive on my desk, and
a note that "we need a diskette driver written for the FTS by Friday."
My introduction to driver design in Unix...by fire.)
ANYWAY, one day the development server just...slowed...to...a...crawl. As
there were a few hundred users, and we were desperately trying to get 5ESS
out the door, this was a Bad Thing(TM). The OS support staff couldn't find
anything wrong with the system; we had everyone who knew anything looking
for the cause.
About this time, a new guy came to me to show me his nifty vi macro. He
was absolutely paranoid about losing anything he was editing if the system
crashed. SO, he wrote a macro that did "sync;sync;sync"...after *every*
keystroke.
We'd found our problem.
Cheers,
--
Dave Ihnat
dih...@dminet.com
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