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Re: Journal Usage



Hi,

On Thu, Nov 08, 2001 at 01:46:57AM -0800, Mike Fedyk wrote:
> > 
> > You can make the journal flush interval longer, so that it will flush only
> 
> And how would I do this safely?  Is it just modifying a define somewhere?

It _ought_ to be that easy, but it's not, yet!

You currently need to modify the line

	journal->j_commit_interval = (HZ * 5);

in linux/fs/jbd/journal.c.  I'll add this as a per-fs tunable.

> > when the journal is getting full, rather than after a fixed amount of time.
> > This may not be ideal either, because if you are forced to flush because
> > the journal is getting full it will likely be just at a time when you want
> > to write into it.
> 
> I'd propose something more gradual besides "oops, the journal is full, let's
> empty it now..."

The advantage to leaving it as long as possible is that you minimise
the amount that needs to be flushed.  If you flush too soon you risk
doing quite a bit of unnecessary IO.

Cheers,
 Stephen





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