Various questions about databases (upgrade and migration)

[Raphaël Halimi]

Hi,

I have a small (3 users) Cyrus IMAP server that started as a very old
Debian (Woody or Sarge, I don't remember exactly) and that I upgraded
through the years, and yesterday I upgraded from Jessie to Stretch
(Cyrus 2.4.17 without caldav, to 2.5.10 with caldav).

As I had some trouble in the past with databases migrations between
BerkeleyDB versions during some upgrades, and although Cyrus started
without any serious problem this time (after minor tuning of some
options in the configuration files), I still wanted to check the state
of the databases.

So, the contents of /usr/lib/cyrus/cyrus-db-types.txt is:

ANNOTATION twoskip
DBENGINE BerkeleyDB5.3
DUPLICATE twoskip
MBOX twoskip
PTS twoskip
QUOTA quotalegacy
SEEN twoskip
STATUSCACHE twoskip
SUBS flat
TLS DEFAULT
TLS twoskip
USERDENY flat
ZONEINFO twoskip

(note that in Debian, no format is forced in /etc/imapd.conf)

So my first questions is: I thought that Cyrus had abandoned BerkeleyDB
a long time ago for skiplist, and then twoskip. Why is it still listed
in this file ? Is there a part of Cyrus that still uses it ?

Now for the databases themselves. In /var/lib/cyrus the global databases
were converted on-the-fly:

# file /var/lib/cyrus/*.db
/var/lib/cyrus/annotations.db:  Cyrus twoskip DB
/var/lib/cyrus/deliver.db:      Cyrus twoskip DB
/var/lib/cyrus/mailboxes.db:    Cyrus twoskip DB
/var/lib/cyrus/statuscache.db:  Cyrus twoskip DB
/var/lib/cyrus/tls_sessions.db: Cyrus twoskip DB
/var/lib/cyrus/user_deny.db:    empty

However, the user databases were not converted:

# file /var/lib/cyrus/user/*/*
/var/lib/cyrus/user/u/user1.seen: Cyrus skiplist DB
/var/lib/cyrus/user/u/user1.sub:  ASCII text
/var/lib/cyrus/user/u/user2.seen:   Cyrus skiplist DB
/var/lib/cyrus/user/u/user2.sub:    ASCII text
/var/lib/cyrus/user/u/user3.seen:   Cyrus skiplist DB
/var/lib/cyrus/user/u/user3.sub:    ASCII text

So my next questions are: why are the databases still in skiplist
format, whereas according to /usr/lib/cyrus/cyrus-db-types.txt, they
should be twoskip ? Why didn't Cyrus convert them on-the-fly like the
global databases ? Do I have to manually do it myself ? And if I do
convert them, will it change anything (performance, reliability, etc etc) ?

Also, what about the various databases in the mail directories
(cyrus.cache, cyrus.header, cyrus.index) ? For most of them, the "file"
command only reports "data". What format are they actually in ? Do I
have to convert them too ?

My last question is about a planned migration of this home server to a
hosted private server. This old server and the new one are now both
Debian Stretch and thus, have the same Cyrus version, but they're not
the same architecture: the old one is i386, and the new one is amd64.

When I mill migrate, will I have to convert the databases through the
flat format and back, or can I blindly copy the whole contents of
/var/spool/cyrus and /var/lib/cyrus to the new server and expect it to
work out of the box ?

Thanks a lot in advance for your answers.

Regards,

-- 
Raphaël Halimi

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