Snapshotting for rollback after updates was[ Re: Drawing lessons from fatal SELinux bug #1054350]

Reindl Harald h.reindl at
Sun Jan 26 19:59:31 UTC 2014

Am 26.01.2014 20:51, schrieb Reindl Harald:
> Am 26.01.2014 20:45, schrieb Chris Murphy:
>>> So ?
>>> It is only visible if you downgrade which a lot of software do not
>>> support and explicitly so
>> The right way to do file format changes is you design the new format. 
>> And in a minor version update, the application gains the ability to 
>> read the new file format, but still writes the old file format. 
>> The major version upgrade of the application is enabled to write the 
>> new file format, while it can read either old or new formats.
> please look at the hidden folders in your userhome and /var/lib/
> to get a picture about what we are talking here
>> If Adobe Photoshop version n.1.0 started to write out Photoshop documents 
>> in a manner that n.0.0 could not read, 100% of users would call it a major bug, 
>> and it would escalate into vicious name calling
> nobody but you is talking about documents the user really visualizes
>> Breaking downward compatibility in file formats for regular Joe user is courting 
>> public relations disaster. It can kill a product. Even Microsoft doesn't do this lightly
> nobody but you is talking about documents the user really visualizes

you may also read

* sqlite is used by a lot of software to store data
* a new feature in a new version may change the scheme
* you do not need care about that
* the new software version recognizes the old format and applies changes
* the old software version may ignore new tables and columns
* it continues to ignore them and don't donwgrade the version info stored somewhere
* the new version after the next update expects consistent data in the new format
* your downgrade and still work with the sqlite database may lead to regret doing so months later

again: *nobody* is talking about documents

and the same which is done with sqlite may be *whatever* format of store internal data
but is affected by the same problematic - *nobody* really supports downgrades

they *may* work fine, there *maybe* are no changes
nobody is telling you so - why? - because what you are doing is not supported

so *please* stop talking about document formats in *that* thread

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