Re: [U2] SIGDANGER

In message 
<513E68AB5AE6D94D981D20663BA074A901C0EC61 <at> MERCURY.INNOVATIONIND.COM>, 
Michael Martin <michael.martin <at> innovationind.com> writes
>Found this on IBM's website.
>
>http://publib.boulder.ibm.com/infocenter/systems/index.jsp?topic=/com.ib
>m.aix.baseadmn/doc/baseadmndita/page_space_trouble.htm
>
>Paging space troubleshooting
>The most common problem regarding paging space is caused by running out
>of allocated space.
>
>The total amount of paging space is often determined by trial and error.
>One commonly used guideline is to double the RAM size and use that
>figure as a paging space target. If paging space runs low, processes can
>be lost, and if paging space runs out, the system can panic. The
>following signal and error information can help you monitor and resolve
>or prevent paging space problems.

I got involved in a little spat over these recommendations. I know I'm 
talking about Linux not AIX here, but ...

Early in either the 2.4 or 2.6 series, Linus decided that the memory 
management code needed sorting out, so he deleted all the error handling 
/ optimisation / "what to do if swap is tight" sort of code. What came 
out of this was that the standard Unix swap algorithm NEEDS twice ram of 
page space to function efficiently.

So if people tell you that the "twice ram" rule is "just a rule of thumb 
you can ignore", well it may or may not be. There certainly WERE very 
good reasons for it - whether those reasons are still valid I don't 
know, but certainly on any system still using the old "traditional" Unix 
algorithms it's still a very good rule you *should* follow - and as a 
*minimum*, not a *target*.

Me - disk space is cheap so I always have swap as a minimum of twice my 
motherboard's maximum ram. Actually, on my current system (max ram = 
768Mb) I've got a 10Gb swap, but I've also got /tmp mounted as a tmpfs 
file system which stuffs the whole lot in ram (or swap, as the case may 
be 

Cheers,
Wol
--

-- 
Anthony W. Youngman <pixie <at> thewolery.demon.co.uk>
'Yings, yow graley yin! Suz ae rikt dheu,' said the blue man, taking the
thimble. 'What *is* he?' said Magrat. 'They're gnomes,' said Nanny. The man
lowered the thimble. 'Pictsies!' Carpe Jugulum, Terry Pratchett 1998
Visit the MaVerick web-site - <http://www.maverick-dbms.org> Open Source Pick
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