2 Using Citadel/UX with Sleepycat (Berkeley) DB
6 [1]Citadel/UX can now use the robust and scalable [2]Berkeley DB from
7 Sleepycat Software as its data store, for increased scalability,
8 reliability, and recoverability.
10 History and introduction
12 From its inception in 1987 until versions 5.1x in 1988,
13 Citadel/UX utilized a built-in data store loosely modelled after Jeff
14 Prothero's original Citadel-CP/M design. But as Citadel systems
15 scaled upwards, supporting Internet-connected systems with heavy
16 concurrent use, and aspirations of becoming a world-class
17 messaging/groupware platform someday, the developers made the decision
18 to switch to an embedded database. The Free Software Foundation's
19 [3]GDBM product was chosen for its simple API and its free license
22 Somewhat less than trouble-free operation from 1988 through 2000,
23 however, proved that GDBM was not the best choice. Heavily utilized
24 systems experienced occasional database corruption, often resulting in
25 repeated crashes of the Citadel server. As a result, we made the
26 decision to switch to [4]Berkeley DB.
28 Berkeley DB offers [5]numerous features which help Citadel/UX to meet
29 its goals as a high-end messaging platform:
30 * Database sizes can scale to hundreds of terabytes
31 * A transaction-based logging system
34 It is clear that Berkeley DB is a better choice than GDBM for a
35 high-utilization database that requires crash recovery. Beginning on
36 December 7, 2000, Citadel/UX supports the use of either GDBM or DB as
37 the data store. At some point in the future, DB will become the
38 default. If you are setting up a potentially busy system, we
39 recommend that you use DB.
42 Building Citadel/UX with DB support
44 Here are the steps required to get Citadel/UX running with Berkeley
45 DB as its back end data store.
47 1. First, you must download and build Berkeley DB itself. Citadel
48 has been developed and tested with DB 3.1.17, which can be
49 downloaded from [6]www.sleepycat.com. Follow the "[7]Building for
50 UNIX" instructions. Make sure that you run the test suite, and
51 perhaps test with some of the sample applications, before moving
53 2. Start with a clean source tree. Either unpack a fresh copy of the
54 source or do a "make distclean" before continuing.
55 3. Run the configure script: ./configure
56 --with-db=/usr/local/BerkeleyDB.3.1 (Specify whatever directory
57 you've actually installed DB into, of course. Also specify any
58 other configure options you need at this time.)
59 4. Run "make" and "make install-exec." Continue installing Citadel
60 as per the instructions supplied with the system.
62 Migrating an existing GDBM-based Citadel to a DB-based Citadel
64 If you have an existing system, you must export your databases,
65 rebuild Citadel with DB support, and then re-import your databases
66 into the new system. Please refer to the document "[8]How to use the
67 importer/exporter" for detailed instructions on this.
69 After you export your database, but before you re-import it, you must
70 perform the following steps:
71 1. Re-build Citadel with DB support, as described above
72 2. Remove all of the *.gdbm files from your data directory.
74 Care and feeding of your DB-powered Citadel
76 Citadel uses the transaction-based logging facility of Berkeley DB.
77 Therefore you will notice log files accumulating in your data
78 directory. These are required for automatic recovery in the event of
79 a catastrophic system failure. Log files have filenames that look
80 like "log.0000000001" whereas the normal database files have names
83 So do you have to keep these log files around forever? No, but there
84 are some rules you should follow:
85 * Don't remove a log file if it's the only log file there.
86 * Don't remove any log file that has a recent timestamp. Generally
87 speaking, if it's more than a week old, and you've been running
88 tape backups every day (you are doing daily backups, right?), you
89 can safely remove the log file.
91 You may think that it's going to keep writing to that one log file
92 forever, but don't panic; when the log file gets sufficiently large it
93 will switch over to another one. As a general rule of thumb, your
94 archival procedure should be to back up to tape every day, and only
95 delete log files that are older than your oldest backup. Berkeley DB
96 supports "hot" backups; in other words, you are permitted to back up
97 your Citadel data without having to first shut down the Citadel
102 1. http://uncensored.citadel.org/citadel
103 2. http://www.sleepycat.com/
104 3. http://www.gnu.org/software/gdbm/gdbm.html
105 4. http://www.sleepycat.com/
106 5. http://www.sleepycat.com/xactfeatures.html
107 6. http://www.sleepycat.com/
108 7. http://www.sleepycat.com/docs/ref/build_unix/intro.html
109 8. http://pixel.citadel.org/citadel/docs/export.html