#include <db_cxx.h> int DbEnv::set_memory_init(DB_MEM_CONFIG type, u_int32_t count);
This method sets the number of objects to allocate and initialize for a specified structure when an environment is created. Doing this helps avoid memory contention after startup. Using this method is optional; failure to use this method causes BDB to allocate a minimal number of structures that will grow dynamically. These structures are all allocated from the main environment region. The amount of memory in this region can be set via the DbEnv::set_memory_max() method. If this method is not called then memory will be limited to the initial settings or by the (deprecated) set maximum interfaces.
The database environment's initialization may also be configured using the environment's DB_CONFIG file. The syntax of the entry in that file is a single line with the string "set_memory_init", one or more whitespace characters, followed by the struct specification, more white space and the count to be allocated. Because the DB_CONFIG file is read when the database environment is opened, it will silently overrule configuration done before that time.
The DbEnv::set_memory_init() method must
be called prior to opening the database environment. It may be
called as often as needed to set the different configurations.
The type parameter must be set to one of the following:
Initialize the number of databases in the environment. This should include each on-disk database and each named in-memory database. If using replication, use the same value on all sites in the replication group.
Initialize the maximum combined length of a database's directory and name strings. For an on-disk database, the database name is the file parameter to the DbEnv::open() method. For a named in-memory database, the database name is the database parameter to the DbEnv::open() method. If using replication, use the same value on all sites in the replication group.
Initialize the number of database files and
subdatabases using external files. This value should
include the number of database files that use
external files but do not contain subdatabases.
This value should also include the number of
subdatabases that use external files. It should
be set in addition to the
DB_MEM_DATABASE value. If using
replication, use the same value on all sites in
the replication group.
Here are some examples of database files with different characteristics and how each database file should affect these values:
DB_MEM_DATABASE.
DB_MEM_DATABASE.
DB_MEM_DATABASE
and add 1 to
DB_MEM_EXTFILE_DATABASE.
DB_MEM_DATABASE
and add 3 to
DB_MEM_EXTFILE_DATABASE.
Initialize locks. A thread uses this structure to lock a page (or record for the QUEUE access method) and hold it to the end of a transaction.
Initialize lock objects. For each page (or record) which is locked in the system, a lock object will be allocated.
Initialize lockers. Each thread which is active in a transactional environment will use a locker structure either for each transaction which is active, or for each non-transactional cursor that is active.
Initialize the log fileid structures. For each database handle which is opened for writing in a transactional environment, a log fileid structure is used.
If using replication, initialize the maximum number of sites in the replication group. Use the same value on all sites in the replication group.
Initialize transaction structures. Each active transaction uses a transaction structure until it either commits or aborts.
Currently transaction structures are not preallocated. This setting will be used to preallocate memory and objects related to transactions such as locker structures and mutexes.
Initialize thread identification structures. If thread tracking is enabled then each active thread will use a structure. Note that since a thread does not signal the BDB library that it will no longer be making calls, unused structures may accumulate until a cleanup is triggered either using a high water mark or by running DbEnv::failchk() .
The count parameter sets the number of specified objects to initialize.
The count specified for locks and lock objects should be at least 5 times the number of lock table partitions. You can examine the current number of lock table partitions configured for your environment using the DbEnv::get_lk_partitions() method.
The DbEnv::set_memory_init()
method may fail and throw a DbException
exception, encapsulating one of the following non-zero errors, or return one
of the following non-zero errors:
If the method was called after DbEnv::open() was called; or if an invalid flag value or parameter was specified.