[U2] AUTO: Jonathan Smith is Out of the Office - But Don't Panic (returning 06/04/2009)

[Jonathan D Smith]

I am out of the office until 06/04/2009.

I am out of the office from the 21st March and will return on the 6th
April. In my absence if you need help with a support related issue please
contact John Jenkins in the UK or Simon Caddick in the USA. If you need
help with a services related matter please contact Ailsa Mcalees in the UK.


Note: This is an automated response to your message  "U2 Users Digest V1
#2574" sent on 21/3/09 8:00:06.

This is the only notification you will receive while this person is away.
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Re: [U2] Does anybody have a hot backup server? {Unclassified}

[Anthony W. Youngman]

In message 
, 
Neil Morris  writes

Hi Mike,

Your inquiry was brought to my attention today.

Could you possibly clarify what is meant by "headers are flushed when they
are updated" in regard to UniVerse dynamic files? Is this in reference to
the information in the T30FILE structure in the UniVerse disk shared memory
segment being written to the header of the file when an update would result
in changing one of the dynamic file parameters stored in the header? Or
does this comment refer to the updated information in the header of the
file being flushed to the physical disk via a sync operation?

If the former, then it is my understanding that UniVerse has always updated
the header immediately when a dynamic file parameter changed and there is
no specific release in which this capability was added. If the latter, the
only way to force the update to be flushed to disk immediately is to have
the file activated for logging with UniVerse Transaction Logging and have
Checkpoint mode enabled.

Perhaps I'm not understanding the question so any clarification you can
provide would be appreciated.


Hi Neil,

It's long been "common knowledge" (which doesn't mean it's correct :-) 
that UV read the dynamic file parameters into memory when the file was 
opened, and didn't always write changed information back until the file 
was closed.


You were therefore advised that it was not safe to copy even a quiescent 
dynamic file at OS level, because the header and data might not be in 
sync.


I remember a posting (from an IBM'er) saying that this had changed round 
about rev 10, and that header and data should now always be in sync on 
disk. (ie the post was about rev 10, the change might have been earlier. 
But the implication was that it *had* been changed.)


Cheers,
Wol
--
Anthony W. Youngman 
'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 -  Open Source Pick
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