Re: [GENERAL] Running with fsync=off

Martijn van Oosterhout <kleptog(at)svana(dot)org> writes:
> On Wed, Dec 21, 2005 at 11:30:15PM -0800, Benjamin Arai wrote:
>> Somebody said running "sync ; sync; sync" from the console. This seems

> The reason is partly historical. On some OSes running sync only starts
> the process but returns immediatly. However, there can only be one sync
> at a time so the second sync waits for the first the finish. The third
> is just for show. However, on Linux at least the one sync is enough.

No, the second and third are both a waste of time. sync tells the
kernel to flush any dirty buffers to disk, but doesn't wait for it to
happen.

There is a story that the advice to type sync twice was originally given
to operators of an early Unix system, as a quick-and-dirty way of making
sure that they didn't power the machine down before the sync completed.
I don't know if it's true or not, but certainly the value would only
appear if you type sync<RETURN>sync<RETURN> so that the first sync is
actually issued before you type the next one. Typing them all on one
line as depicted is just a waste of finger motion.

regards, tom lane