[firebase-br] Perda de dados 2 dias

Carlos H. Cantu listas em warmboot.com.br
Ter Dez 22 22:46:54 -03 2009

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Disappeared” files on Linux/Unix/HP-UX/...

It is well-known fact that Linux uses the inode mechanism to support
different file systems. One of the key features of this mechanism is
the use of cache to handle file descriptors – it means that file
descriptors are stored both in memory and on disk.

To InterBase and Firebird it brings an onerous side-effect. If you
replace a database when users are still connected, the server will
continue to work with the old file, which is wrongly assumed to be
deleted. The danger here is that, when the last user detaches, the
server will drop the file forever and the “new” file steps in to
replace it at that point. You never know it has happened until it is
too late and then, it is most likely to be discovered by furious
users: “Where is my work from last week?!”

The longest period of lost data due to such «disappearing» that I have
observed was 1.5 years. It was a multi-volume database on Linux and
one of the 4Gb volumes was completely lost.

You may say it is a very rare circumstance but I can stake a case of
beer on the fact that, right now, at least one hundred server
installations have this problem. We receive at least one repair
request due to this problem every two months!

Carlos H. Cantu
www.FireBase.com.br - www.firebirdnews.org
www.warmboot.com.br - blog.firebase.com.br

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