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
(8) for upgrade instructions.
To build ovdb support into INN, specify the option --with-bdb
running the configure script. By default, configure will search for
Berkeley DB in default search paths; there will be a message in the
configure output indicating the pathname that will be used.
You can override this pathname by adding a path to the option, for instance
. This directory is expected to have
are also checked), containing respectively db.h
, and the library
itself. In case non-standard paths to the Berkeley DB libraries are
used, one or both of the options --with-bdb-include
can be given to configure with a path.
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
"ovdb". The ovdb database is stored in the directory specified by
parameter 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
) 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
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
- 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
- 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
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
If compression is not enabled (either from the "compress" option in
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
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
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:
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 database.
For example, let's say that you have pathoverview
and you have four additional file systems created on
. You would create a file "/mnt/overview/DB_CONFIG"
containing the following lines:
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 directories.
Whenever you change DB_CONFIG or move database files around, make sure all news
processes that use the database are shut down first (including nnrpds).
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, rc.news
will invoke ovdb_init
must be run before using the database. It performs the
- 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 shutdown.
- Starts the DB housekeeping processes (ovdb_monitor)
if they're not already running.
And when stopping INN, rc.news
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
INN programs that use overview will fail to start up if the ovdb_monitor
processes aren't running. Be sure to run ovdb_init
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.
should perform a recovery operation which will remove the
locks and repair damage caused by killing the deadlocked processes.
- The ovmethod and pathoverview parameters are
relevant to ovdb.
- Optional configuration file for tuning. See CONFIGURATION
- Directory where the database goes. Berkeley DB calls
it the 'DB_HOME' directory.
- Optional file to configure the layout of the database
- 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 <email@example.com> for InterNetNews
$Id: ovdb.pod 9593 2013-12-27 21:16:09Z iulius $
Berkeley DB documentation: in the docs
directory of the
Berkeley DB source distribution, or on the Oracle Berkeley DB