[Zope3-dev] Tossing Data.fs considered harmful

[Jeremy Hylton]

On Sat, 2003-03-15 at 16:19, Tres Seaver wrote:
> Jeremy's note about the opaque pickles said, "If this is going to cause
> anyone heartache, please let us know ASAP."  I did not construe that as
> an offer to write a conversion script, but rather as an offer to
> negotiate about when the branch would land.

It's all a question of negotiation.  Writing a conversion script is
extra work for me.  If no one cares about tossing their Data.fs, then I
don't want to waste time doing useless work.  Same goes for a minor
inconvenience.  If anyone was going to suffer real hardship or
heartache, then I would have written a conversion script.

It's relatively easy for Barry and I to handle migration issues.  Most
of the time we've just got to manipulate a bunch of opaque pickles.  At
worst, we sniff a few of them.  I expect we could even write a
conversion script from ZODB3 databases to ZODB4 databases without too
much hassle.  But the cost of writing conversion scripts for each
incremental change adds up.

I think people reorganizing higher level services will have more
trouble.  They've actually got to worry about the contents of the
pickles -- relationships among objects, removed and renamed classes,
etc.

I wonder if a reasonable middle ground is to offer conversion utilities
between each milestone release.  Each time we release version N+1, we
provide an upgrade script that deals with data from version N.  If
someone wants to develop applications on top of Zope, they ned to stick
to milestone releases.

Jeremy