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Re: Data loss: suggestions for handling



Roland Mas wrote:
> key-value pairs.  One of the keys (okay, the only one normally) is
> "db-version", and the corresponding value is a version number with the
> same semantics as the one provided by dpkg for the ordering).  When I
> need to upgrade something, I go the following steps:
> 
> ,----[ One upgrade chunk ]
> | Begin transaction
> | Do stuff
> | Check that stuff went fine (and raise an exception/abort if not)
> | Update the value for db-version
> | Commit transaction
> `----
> 
> This is of course only executed if current db-version is less than
> targeted version.  So I have a series of upgrade chunks, arranged like
> this:
> 
> ,----[ Upgrade script ]
> | $target version = 1.0
> | if (current-version < $target-version) {
> |    Do the upgrade chunk for target=$target-version
> | }
> | 
> | $target version = 1.1
> | if (current-version < $target-version) {
> |    Do the upgrade chunk for target=$target-version
> | }
> | 
> | $target version = 1.4
> | if (current-version < $target-version) {
> |    Do the upgrade chunk for target=$target-version
> | }
> `----
> 
>   The postinst script always runs this upgrade script.  So all the
> steps that were previously completed are not replayed, and you'll
> start at the first one that hasn't been successfully run yet. 

Heh, that's funny, this is exactly the approach I use for mooix database
upgrades. Even my code looks scarily similar to yours, although I don't
have transactons and just try to make it all idempotent instead.

-- 
see shy jo

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