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Re: Journal Usage



On Mon, Nov 05, 2001 at 09:26:58AM -0700, Andreas Dilger wrote:
> On Nov 02, 2001  18:36 -0800, Mike Fedyk wrote:
> > I have a large journal of 400MB (the max for 4k blocks), and I'd like to be
> > able to check how much of it is being used.
> 
> I don't think it is currently possible to do this.
>

:( Any plans to do so?  As Nigel said, it would be very useful for external
journals...

> > If it's not being used that much, I'd like to know if the writes *from* the
> > journal to the rest of the disk could be delayed until a certain percentage
> > of the journal has been used.
> >
> > It would be nice to be able to get more contiguous writes to the journal for
> > bursty types of loads...
> 
> You can make the journal flush interval longer, so that it will flush only
> 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 suppose if you find that the large journal is not even close to filling
> up you could increase the flush interval until it fills to about 1/5
> full under normal usage.  It will flush itself when it reaches 1/4 full,
> so this gives you a bit of a window to flush an idle journal.
>

I was thinking of using watermarks...  ie, 10% start flushing lightly but
not while writing to the journal, 50% don't worry about mixing writes to
journal and flushing journal, 70% all out flush of the journal trying to get
it below 40%...

Of course these numbers could be adjusted for performance, and probably
should very mased on journal size...

Mike





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