[Zope] Thousands of Objects - how do they manifest? (newbie)

[Paul Winkler]

On Mon, Jan 06, 2003 at 12:48:22PM -0500, Casey Duncan wrote:
> As for restoration, FileStorage is pretty resilient to data loss due to the 
> fact that it only appends transactions to the file.

The last time this subject came up, there was a quibble about this
that made me perhaps overly cautious about assuming the above is true. 
I've dug it out of the archives and read it more closely now. Summary:
NORMALLY zope & FileStorage only append to the file, but it
is conceivable that a third-party Zope product might alter this.
I don't know which, if any, Products actually do this.

Here's the message from the zope@zope.org archive:

Toby Dickenson wrote:
> On Monday 28 October 2002 1:41 am, Jens Vagelpohl wrote:
>> FileStorage only appends at the end of the file. 
>
> Not entirely true. FileStorage still supports a non-transactional undo 
> mechanism that writes bytes to the middle of files. This mechanism is not 
> normally used by Zope, however it might be used by other non-Zope ZODB 
> applications, or custom products. 
> 
> (could it be exploited by an attacker who wanted to break your backups? hmmmm)
> 
> Proviing that this type of live backup is safe requires knowledge about how 
> the backup program will read the file. The obvious approach of reading from 
> start to end is compatible with FileStorages append-only approach, but not 
> all backup programs operate that way. I prefer to take a copy of the data.fs 
> using 'cp' (which I know to be safe), and backup that.

-- 

Paul Winkler
http://www.slinkp.com
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