We expect to upgrade from Roundcube 0.9.5 to 1.0.x over the summer 
vacation (my management chain and I prefer not to make substantial 
changes during the academic year).
Something that I would like to do if possible is have a period of 
parallel running so that people can kick the tires and make sure that 
our small collection of local plugins and our local skin are working 
correctly for a few days or weeks before we commit to running the new 
version.
I can of course dump and restore the existing Roundcube database to 
build a completely independent Roundcube 1.0.1 test system off to one 
side, away from the production servers.
However if I look at the handful of database upgrade steps from 0.9.5 to 
1.0.1, the only significant change would appear to be the attached 
renaming of sequences (we aren't using any of the cache tables).
   .../SQL/postgres/2013042700.sql :
   ALTER SEQUENCE user_ids RENAME TO users_seq;
   ALTER TABLE users ALTER COLUMN user_id SET DEFAULT 
nextval('users_seq'::text);
   ALTER SEQUENCE identity_ids RENAME TO identities_seq;
   ALTER TABLE identities ALTER COLUMN identity_id SET DEFAULT 
nextval('identities_seq'::text);
   ALTER SEQUENCE contact_ids RENAME TO contacts_seq;
   ALTER TABLE contacts ALTER COLUMN contact_id SET DEFAULT 
nextval('contacts_seq'::text);
   ALTER SEQUENCE contactgroups_ids RENAME TO contactgroups_seq;
   ALTER TABLE contactgroups ALTER COLUMN contactgroup_id SET DEFAULT 
nextval('contactgroups_seq'::text);
   ALTER SEQUENCE search_ids RENAME TO searches_seq;
   ALTER TABLE searches ALTER COLUMN search_id SET DEFAULT 
nextval('searches_seq'::text);
These sequence names appear to be hard-wired in 1.0.1.
However Roundcube 0.9.5 can be reconfigured to use any names, including 
the names used by 1.0.1:
  // you can define specific sequence names used in PostgreSQL
  $rcmail_config['db_sequence_users'] = 'users_seq';
  $rcmail_config['db_sequence_identities'] = 'identities_seq';
  $rcmail_config['db_sequence_contacts'] = 'contacts_seq';
  $rcmail_config['db_sequence_contactgroups'] = 'contactgroups_seq';
  $rcmail_config['db_sequence_searches'] = 'searches_seq';
A brief experiment on a test system suggests that I can safely switch 
back and forth between Roundcube 0.9.5 and 1.0.1 with this single 
configuration change at the 0.9.5 end.
My question is whether this is a sensible thing to try and do. Are there 
incompatible changes in the various preferences databases which aren't 
reflected in the database schema? That would require an independent test 
system.
Thanks,
-- 
David Carter                             Email: 
David.Carter(a)uis.cam.ac.uk
University of Cambridge,                 Phone: (01223) 334502
Information Services,                    Fax:   (01223) 334679
7 J J Thomson Avenue,
Cambridge UK.  CB3 0RB