|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 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.|
|compress||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.|
|numdbfiles||Overview data is split between this many files. Currently, innd will keep all of the files open, so dont 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.|
|txn_nosync||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.|
|useshm||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 false.|
|shmkey||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.|
|pagesize||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:
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.
|maxlocks||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 expireovers 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.
|numrsprocs||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.|
|maxrsconn||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 cant 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:
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 wont be created automatically. Also, dont 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, lets 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 lines:
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 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 youre running.
When starting the news system, rc.news will invoke ovdb_init. ovdb_init must be run before using the database. It performs the following tasks:
And when stopping INN, rc.news kills the ovdb_monitor processes after the other INN processes have been shut down.
o Creates the database environment, if necessary. o 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. o Starts the DB housekeeping processes (ovdb_monitor) if theyre not already running.
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 arent 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 processes.
inn.conf The ovmethod and pathoverview parameters are relevant to ovdb. ovdb.conf Optional configuration file for tuning. See CONFIGURATION above. pathoverview Directory where the database goes. Berkeley DB calls it the DB_HOME directory. pathoverview/DB_CONFIG Optional file to configure the layout of the database files. pathrun/ovdb.sem 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. pathrun/ovdb_monitor.pid 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 $
inn.conf(5), innd(8), nnrpd(8), ovdb_init(8), ovdb_monitor(8), ovdb_stat(8)
Berkeley DB documentation: in the docs directory of the Berkeley DB source distribution, or on the Oracle Berkeley DB web page (http://www.oracle.com/technetwork/database/database-technologies/berkeleydb/overview/index.html <http://www.oracle.com/technetwork/database/database-technologies/berkeleydb/overview/index.html>).
|INN 2.6.0||OVDB (5)||2015-09-12|