ovdb(5)

NAME
ovdb - Overview storage method for INN

DESCRIPTION
Ovdb is a storage method that uses the BerkeleyDB library to store overview data. It requires version 2.6.x or later of the BerkeleyDB library; it is known to work well with version 2.7.7. There is also a 3.0.55, but it is not very stable (though ovdb will compile correctly with it). Check the web page http://www.avalon.net/~hakehoe/inn/ for the latest on BerkeleyDB compatibility.

Ovdb makes use of the full transaction/logging/locking functionality of the BerkeleyDB environment. BerkeleyDB may be downloaded from http://www.sleepycat.com .

The BerkeleyDB distribution is (by default) installed into /usr/local/BerkeleyDB, with subdirectories lib/, include/, and bin/ for the library, headers, and support tools, respectively. Version 3.x uses /usr/local/BerkeleyDB.3.x instead. Ovdb uses some of the support tools in the bin/ subdirectory; namely db_archive, db_checkpoint, and db_deadlock.

INSTALLATION
To build ovdb support into INN, specify the option `--with-berkeleydb' when running the configure script. By default, configure will search for a BerkeleyDB tree in several likely locations, and choose the highest version (based on the name of the directory, e.g., BerkeleyDB.3.0) that it finds. There will be a message in the configure output indicating the chosen pathname.

You can override this pathname by adding a path to the option, e.g., `--with-berkeleydb=/usr/BerkeleyDB.3.1'. This directory is expected to have subdirectories include, lib, and bin containing db.h, the library itself, and the db_* utilities, respectively.

The ovdb database will take up more disk space for a given spool than the other overview methods. Plan on needing at least 1.1 KB for every article in your spool (not counting crossposts). So, if you have 5 million articles, you'll need at least 5.5 GB of disk space for ovdb. With BerkeleyDB 2.x, the db files are 'grow only'; the library will not shrink them, even if data is removed. So, reserving extra space above the estimate is a good idea. Plus, you'll need additional space for transaction logs: at least 40 MB, preferably 100 MB or more. (The logs may be on a different filesystem -- see the DB_CONFIG section.)

CONFIGURATION
To enable ovdb, set the ovmethod parameter in inn.conf to `ovdb'. The ovdb database is stored in the directory specified by the pathoverview paramter in inn.conf. This is the "DB_HOME" directory. To start out, this directory should be empty (other than an optional DB_CONFIG file, see the DB_CONFIG section for details) and innd (or makehistory) will create the files as necessary in that directory.

Other parameters for configuring ovdb are in the optional ovdb.conf configuration file. See also the sample ovdb.conf.

numdbfiles
    Overview data is split between this many files. Currently, innd will keep all of the files open, so don't set this too high or innd may run out of file descriptors. The nnrpds only open one at a time, regardless. May be set to one, or just a few, but only do that if your OS supports large (>2G) files. Warning: do NOT change this on an already established database. Default is 32.

txn_nosync
    If txn_nosync is set to false, BerkeleyDB flushes the log after every transaction. This minimizes the number of transactions that may be lost in the event of a crash, but results in significantly degraded performance. Default is true.

cachesize
    Size of the memory pool cache, in Kilobytes. The cache will have a backing store file in the DB directory which will be at least as big. In general, the bigger the cache, the better. Use `db_stat -m' to see cache hit percentages. If they're less than 80%, try increasing the cache size. To make a change of this parameter take effect with an existing database, remove the __db* files while there are no database processes running. Default is 8000 K, which may be adequate for small to medium-sized servers. Full-feed servers will probably need at least 14000.

pagesize
    Sets the page size for the DB files (in bytes). Must be a power of 2. Best choices are 4096, 8192, or 16384. The default is 8192. You can not change the pagesize of an existing DB, it must be recreated.

minkey
    Sets the minimum number of keys per page. See the BerkeleyDB documentation for more info. Default is based on page size:

     default_minkey = pagesize / 2048
    You can not change the minkey of an existing DB, it must be recreated.

  DB_CONFIG
A file called DB_CONFIG may be placed in the database directory to customize where the various database files and transaction logs are written. By default, all of the files are written in the "DB_HOME" directory. One way to improve performance is to put the transaction logs on a different disk. To do this, put:

DB_LOG_DIR /path/to/logs

in the DB_CONFIG file. If the pathname you give starts with a /, it is treated as an absolute path; otherwise, it is relative to the "DB_HOME" directory. Make sure that any directories you specify exist and have proper ownership/mode before starting INN, because they won't be created automatically. Also, don't change the DB_CONFIG file while anything that uses ovdb is running.

The DB_CONFIG functionality is part of BerkeleyDB itself.

RUNNING
You don't need to do anything special when starting or stopping INN when using ovdb, as long as you use rc.news. When starting, rc.news:

•   Runs `ovdb_recover'. This will perform any needed recovery on the database; e.g., if there was a crash that may have left the database in an inconsistent state. This is done before innd is started. If the innd.pid file is present but innd is not running (i.e., unclean shutdown), rc.news will supply the `-f' argument to `ovdb_recover'

•   Runs `dbprocs start'. This starts the DB housekeeping processes.

And when stopping INN, rc.news calls `dbprocs stop' after the other INN processes have been shut down.

DIAGNOSTICS
Problems relating to ovdb are logged to news.err with "OVDB" in the error message.

If a program accessing the database crashes, or otherwise exits uncleanly, it might leave a stale lock in the database. This lock could cause other processes to deadlock on that stale lock. To fix this, shut down all news processes (using `kill -9' if necessary) then run `ovdb_recover -f' as the news user, e.g.: `su news -c "/PATHBIN/ovdb_recover -f"' This will remove all locks plus repair any damage caused by killing deadlocked processes.

FILES

inn.conf
    The ovmethod and pathoverview parameters are relevant to ovdb.

ovdb.conf
    Optional configuration file for tuning. See CONFIGURATION section above.

pathoverview
    Directory where the database goes. BerkeleyDB calls it the 'DB_HOME' directory.

pathoverview/DB_CONFIG
    Optional file to configure the layout of the database files.

TO DO
I've modified innshellvars and innshellvars.pl to add the BerkeleyDB bin dir to PATH and set DB_HOME to innconf->pathoverview. Since I don't know TCL, someone needs to modify innshellvars.tcl in the same way.

Implement a way to limit how many databases can be open at once (to reduce file descriptor usage); maybe using something similar to the cache code in ov3.c

HISTORY
Written by Heath Kehoe <hakehoe@avalon.net> for InterNetNews

SEE ALSO
rc.news(8), inn.conf(5), dbprocs(8), ovdb_recover(8), ovdb_upgrade(8)

BerkeleyDB documentation, in the docs directory of the BerkeleyDB source distribution, or on the Sleepycat web page: http://www.sleepycat.com/