Using Citadel/UX with Sleepycat (Berkeley) DB
                                      
Abstract

   [1]Citadel/UX can now use the robust and scalable [2]Berkeley DB from
   Sleepycat Software as its data store, for increased scalability,
   reliability, and recoverability.
   
History and introduction

   From its inception in 1987 until versions 5.1x in 1988,
   Citadel/UX utilized a built-in data store loosely modelled after Jeff
   Prothero's original Citadel-CP/M design.  But as Citadel systems
   scaled upwards, supporting Internet-connected systems with heavy
   concurrent use, and aspirations of becoming a world-class
   messaging/groupware platform someday, the developers made the decision
   to switch to an embedded database.  The Free Software Foundation's
   [3]GDBM product was chosen for its simple API and its free license
   (the LGPL).
   
   Somewhat less than trouble-free operation from 1988 through 2000,
   however, proved that GDBM was not the best choice.  Heavily utilized
   systems experienced occasional database corruption, often resulting in
   repeated crashes of the Citadel server.  As a result, we made the
   decision to switch to [4]Berkeley DB.
   
   Berkeley DB offers [5]numerous features which help Citadel/UX to meet
   its goals as a high-end messaging platform:
     * Database sizes can scale to hundreds of terabytes
     * A transaction-based logging system
     * Recovery utilities
       
   It is clear that Berkeley DB is a better choice than GDBM for a
   high-utilization database that requires crash recovery.  Beginning on
   December 7, 2000, Citadel/UX supports the use of either GDBM or DB as
   the data store.  At some point in the future, DB will become the
   default.  If you are setting up a potentially busy system, we
   recommend that you use DB.
   
   
Building Citadel/UX with DB support

   Here are the steps required to get Citadel/UX running with Berkeley
   DB as its back end data store.
   
    1. First, you must download and build Berkeley DB itself.  Citadel
       has been developed and tested with DB 3.1.17, which can be
       downloaded from [6]www.sleepycat.com.  Follow the "[7]Building for
       UNIX" instructions.  Make sure that you run the test suite, and
       perhaps test with some of the sample applications, before moving
       on.
    2. Start with a clean source tree.  Either unpack a fresh copy of the
       source or do a "make distclean" before continuing.
    3. Run the configure script:  ./configure
       --with-db=/usr/local/BerkeleyDB.3.1   (Specify whatever directory
       you've actually installed DB into, of course.  Also specify any
       other configure options you need at this time.)
    4. Run "make" and "make install-exec."  Continue installing Citadel
       as per the instructions supplied with the system.
       
Migrating an existing GDBM-based Citadel to a DB-based Citadel

   If you have an existing system, you must export your databases,
   rebuild Citadel with DB support, and then re-import your databases
   into the new system.  Please refer to the document "[8]How to use the
   importer/exporter" for detailed instructions on this.
   
   After you export your database, but before you re-import it, you must
   perform the following steps:
    1. Re-build Citadel with DB support, as described above
    2. Remove all of the *.gdbm files from your data directory.
       
Care and feeding of your DB-powered Citadel

   Citadel uses the transaction-based logging facility of Berkeley DB.
   Therefore you will notice log files accumulating in your data
   directory.  These are required for automatic recovery in the event of
   a catastrophic system failure.  Log files have filenames that look
   like "log.0000000001" whereas the normal database files have names
   like "cdb.05".
   
   So do you have to keep these log files around forever?  No, but there
   are some rules you should follow:
     * Don't remove a log file if it's the only log file there.
     * Don't remove any log file that has a recent timestamp.  Generally
       speaking, if it's more than a week old, and you've been running
       tape backups every day (you are doing daily backups, right?), you
       can safely remove the log file.
       
   You may think that it's going to keep writing to that one log file
   forever, but don't panic; when the log file gets sufficiently large it
   will switch over to another one.  As a general rule of thumb, your
   archival procedure should be to back up to tape every day, and only
   delete log files that are older than your oldest backup.  Berkeley DB
   supports "hot" backups; in other words, you are permitted to back up
   your Citadel data without having to first shut down the Citadel
   server.

References

   1. http://uncensored.citadel.org/citadel
   2. http://www.sleepycat.com/
   3. http://www.gnu.org/software/gdbm/gdbm.html
   4. http://www.sleepycat.com/
   5. http://www.sleepycat.com/xactfeatures.html
   6. http://www.sleepycat.com/
   7. http://www.sleepycat.com/docs/ref/build_unix/intro.html
   8. http://pixel.citadel.org/citadel/docs/export.html