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       ovdb - Overview storage method for INN


       Ovdb is a storage method that uses the Berkeley DB library to store
       overview data.  It requires version 4.4 or later of the Berkeley DB
       library (4.7+ is recommended because older versions suffer from various

       Ovdb makes use of the full transaction/logging/locking functionality of
       the Berkeley DB environment.  Berkeley DB may be downloaded from
       <> and is needed to build the ovdb backend.


       This is version 2 of ovdb.  If you have a database created with a
       previous version of ovdb (such as the one shipped with INN 2.3.0) your
       database will need to be upgraded using ovdb_init(8).  See the man page
       ovdb_init(8) for upgrade instructions.


       To build ovdb support into INN, specify the option --with-berkeleydb
       when running the configure script.  By default, configure will search
       for a Berkeley DB tree in several likely locations, and choose the
       highest version (based on the name of the directory, e.g.,
       BerkeleyDB.4.4) 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.4.4.  This directory is expected to
       have subdirectories include and lib, containing db.h, and the library
       itself, respectively.

       The ovdb database may 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 compression enabled, this estimate changes to 0.7 KB per article.
       See the COMPRESSION section below.  Plus, you’ll need additional space
       for transaction logs: at least 100 MB.  By default the transaction logs
       go in the same directory as the database.  To improve performance, they
       can be placed on a different disk -- see the DB_CONFIG section.


       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 DB_CONFIG for details) and innd (or makehistory) will create the
       files as necessary in that directory.  Make sure the directory is owned
       by the news user.

       Other parameters for configuring ovdb are in the ovdb.conf(5)
       configuration file.  See also the sample ovdb.conf.

           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 "ovdb_stat
           -m" to see cache hit percentages.  To make a change of this
           parameter take effect, shut down and restart INN (be sure to kill
           all of the nnrpds when shutting down).  Default is 8000, which is
           adequate for small to medium sized servers.  Large servers will
           probably need at least 20000.

           If INN was compiled with zlib, and this compress parameter is true,
           OVDB will compress overview records that are longer than 600 bytes.
           See the COMPRESSION section below.

           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.  nnrpd only opens 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.  Changing this parameter has no
           effect on an already-established database.  Default is 32.

           If txn_nosync is set to false, Berkeley DB 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.

           If useshm is set to true, Berkeley DB will use shared memory
           instead of mmap for its environment regions (cache, lock, etc).
           With some platforms, this may improve performance.  Default is

           Sets the shared memory key used by Berkeley DB when ’useshm’ is
           true.  Berkeley DB will create several (usually 5) shared memory
           segments, using sequentially numbered keys starting with ’shmkey’.
           Choose a key that does not conflict with any existing shared memory
           segments on your system.  Default is 6400.

           Sets the page size for the DB files (in bytes).  Must be a power of
           2.  Best choices are 4096 or 8192.  The default is 8192.  Changing
           this parameter has no effect on an already-established database.

           Sets the minimum number of keys per page.  See the Berkeley DB
           documentation for more info.  Default is based on page size and
           whether compression is enabled:

              default_minkey = MAX(2, pagesize / 2600) if compress is false
              default_minkey = MAX(2, pagesize / 1500) if compress is true

           The lowest allowed minkey is 2.  Setting minkey higher than the
           default is not recommended, as it will cause the databases to have
           a lot of overflow pages.  Changing this parameter has no effect on
           an already-established database.

           Sets the Berkeley DB "lk_max" parameter, which is the maximum
           number of locks that can exist in the database at the same time.
           Default is 4000.

           The nocompact parameter affects expireover’s behavior.  The
           expireover function in ovdb can do its job in one of two ways:  by
           simply deleting expired records from the database, or by re-writing
           the overview records into a different location leaving out the
           expired records.  The first method is faster, but it leaves ’holes’
           that result in space that can not immediately be reused.  The
           second method ’compacts’ the records by rewriting them.

           If this parameter is set to 0, expireover will compact all
           newsgroups; if set to 1, expireover will not compact any
           newsgroups; and if set to a value greater than one, expireover will
           only compact groups that have less than that number of articles.

           Experience has shown that compacting has minimal effect (other than
           making expireover take longer) so the default is now 1.  This
           parameter will probably be removed in the future.

           Normally, each nnrpd process directly accesses the Berkeley DB
           environment.  The process of attaching to the database (and
           detaching when finished) is fairly expensive, and can result in
           high loads in situations when there are lots of reader connections
           of relatively short duration.

           When the readserver parameter is true, the nnrpds will access
           overview via a helper server (ovdb_server -- which is started by
           ovdb_init).  This can also result in cleaner shutdowns for the
           database, improving stability and avoiding deadlocks and corrupted
           databases.  If you are experiencing any instability in ovdb, try
           setting this parameter to true.  Default is false.

           This parameter is only used when readserver is true.  It sets the
           number of ovdb_server processes.  As each ovdb_server can process
           only one transaction at a time, running more servers can improve
           reader response times.  Default is 5.

           This parameter is only used when readserver is true.  It sets a
           maximum number of readers that a given ovdb_server process will
           serve at one time.  This means the maximum number of readers for
           all of the ovdb_server processes is (numrsprocs * maxrsconn).  This
           does not limit the actual number of readers, since nnrpd will fall
           back to opening the database directly if it can’t connect to a
           readserver.  Default is 0, which means an umlimited number of
           connections is allowed.


       New in this version of OVDB is the ability to compress overview data
       before it is stored into the database.  In addition to consuming less
       disk space, compression keeps the average size of the database keys
       smaller.  This in turn increases the average number of keys per page,
       which can significantly improve performance and also helps keep the
       database more compact.  This feature requires that INN be built with
       zlib. Only records larger than 600 bytes get compressed, because that
       is the point at which compression starts to become significant.

       If compression is not enabled (either from the "compress" option in
       ovdb.conf or INN was not built from zlib), the database will be
       backward compatible with older versions of OVDB.  However, if
       compression is enabled, the database is marked with a newer version
       that will prevent older versions of OVDB from opening the database.

       You can upgrade an existing database to use compression simply by
       setting compress to true in ovdb.conf.  Note that existing records in
       the database will remain uncompressed; only new records added after
       enabling compression will be compressed.

       If you disable compression on a database that previously had it
       enabled, new records will be stored uncompressed, but the database will
       still be incompatible with older versions of OVDB (and will also be
       incompatible with this version of OVDB if it was not built with zlib).
       So to downgrade to a completely uncompressed database you will have to
       rebuild the database using makehistory.


       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.

       Another thing that you can do with this file is to split the overview
       database across multiple disks.  In the DB_CONFIG file, you can list
       directories that Berkeley DB will search when it goes to open a

       For example, let’s say that you have pathoverview set to /mnt/overview
       and you have four additional file systems created on /mnt/ov?.  You
       would create a file "/mnt/overview/DB_CONFIG" containing the following

           set_data_dir /mnt/overview
           set_data_dir /mnt/ov1
           set_data_dir /mnt/ov2
           set_data_dir /mnt/ov3
           set_data_dir /mnt/ov4

       Distribute your ovNNNNN files into the four filesystems.  (say, 8
       each).  When called upon to open a database file, the db library will
       look for it in each of the specified directories (in order).  If said
       file is not found, one will be created in the first of those

       Whenever you change DB_CONFIG or move database files around, make sure
       all news processes that use the database are shut down first (including

       The DB_CONFIG functionality is part of Berkeley DB itself, rather than
       something provided by ovdb.  See the Berkeley DB documentation for
       complete details for the version of Berkeley DB that you’re running.


       When starting the news system, will invoke ovdb_init.
       ovdb_init must be run before using the database.  It performs the
       following tasks:

       ·   Creates the database environment, if necessary.

       ·   If the database is idle, it performs a normal recovery.  The
           recovery will remove stale locks, recreate the memory pool cache,
           and repair any damage caused by a system crash or improper

       ·   Starts the DB housekeeping processes (ovdb_monitor) if they’re not
           already running.

       And when stopping INN, kills the ovdb_monitor processes after
       the other INN processes have been shut down.


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

       INN programs that use overview will fail to start up if the
       ovdb_monitor processes aren’t running.  Be sure to run ovdb_init before
       running anything that accesses overview.

       Also, INN programs that use overview will fail to start up if the user
       running them is not the "news" user.

       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) and
       then restart.  ovdb_init should perform a recovery operation which will
       remove the locks and repair damage caused by killing the deadlocked


           The ovmethod and pathoverview parameters are relevant to ovdb.

           Optional configuration file for tuning.  See CONFIGURATION above.

           Directory where the database goes.  Berkeley DB calls it the
           ’DB_HOME’ directory.

           Optional file to configure the layout of the database files.

           A file that gets locked by every process that is accessing the
           database.  This is used by ovdb_init to determine whether the
           database is active or quiescent.

           Contains the process ID of ovdb_monitor.


       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


       Written by Heath Kehoe <> for InterNetNews

       $Id: ovdb.pod 8334 2009-02-20 20:18:37Z iulius $


       inn.conf(5), innd(8), nnrpd(8), ovdb_init(8), ovdb_monitor(8),

       Berkeley DB documentation: in the docs directory of the Berkeley DB
       source distribution, or on the Sleepycat web page: