Berkeley DB Reference Guide: Database environment introduction

Berkeley DB Reference Guide:
Environment

Database environment introduction

A Berkeley DB environment is an encapsulation of one or more databases, log files and region files. Region files are the shared memory areas that contain information about the database environment such as memory pool cache pages. Only databases are byte-order independent and only database files can be moved between machines of different byte orders. Log files can be moved between machines of the same byte order. Region files are usually unique to a specific machine and potentially to a specific operating system release.

The simplest way to administer a Berkeley DB application environment is to create a single home directory that stores the files for the applications that will share the environment. The environment home directory must be created before any Berkeley DB applications are run. Berkeley DB itself never creates the environment home directory. The environment can then be identified by the name of that directory.

An environment may be shared by any number of processes, as well as by any number of threads within those processes. It is possible for an environment to include resources from other directories on the system, and applications often choose to distribute resources to other directories or disks for performance or other reasons. However, by default, the databases, shared regions (the locking, logging, memory pool, and transaction shared memory areas) and log files will be stored in a single directory hierarchy.

It is important to realize that all applications sharing a database environment implicitly trust each other. They have access to each other's data as it resides in the shared regions, and they will share resources such as buffer space and locks. At the same time, any applications using the same databases must share an environment if consistency is to be maintained between them.

Database Environment Operations	Description
db_env_create	Create an environment handle
DB->get_env	Return DB's underlying DB_ENV handle
DB_ENV->close	Close an environment
DB_ENV->dbremove	Remove a database
DB_ENV->dbrename	Rename a database
DB_ENV->err, DB_ENV->errx	Error message
DB_ENV->failchk	Check for thread failure
DB_ENV->fileid_reset	Reset database file IDs
DB_ENV->get_home	Return environment's home directory
DB_ENV->get_open_flags	Return flags with which the environment was opened
DB_ENV->lsn_reset	Reset database file LSNs
DB_ENV->open	Open an environment
DB_ENV->remove	Remove an environment
DB_ENV->stat_print	Environment statistics
db_strerror	Error strings
db_version	Return version information
Environment Configuration
DB_ENV->set_alloc	Set local space allocation functions
DB_ENV->set_app_dispatch	Configure application recovery
DB_ENV->set_cachesize	Set the environment cache size
DB_ENV->set_data_dir	Set the environment data directory
DB_ENV->set_encrypt	Set the environment cryptographic key
DB_ENV->set_errcall, DB_ENV->set_msgcall	Set error and informational message callbacks
DB_ENV->set_errfile, DB_ENV->set_msgfile	Set error and informational message FILE
DB_ENV->set_errpfx	Set error message prefix
DB_ENV->set_event_notify	Set event notification callback
DB_ENV->set_feedback	Set feedback callback
DB_ENV->set_flags	Environment configuration
DB_ENV->set_isalive	Set thread is-alive callback
DB_ENV->set_intermediate_dir_mode	Set intermediate directory creation mode
DB_ENV->set_rpc_server	Establish an RPC server connection
DB_ENV->set_shm_key	Set system memory shared segment ID
DB_ENV->set_thread_id	Set thread of control ID function
DB_ENV->set_thread_count	Set approximate thread count
DB_ENV->set_thread_id_string	Set thread of control ID format function
DB_ENV->set_timeout	Set lock and transaction timeout
DB_ENV->set_tmp_dir	Set the environment temporary file directory
DB_ENV->set_verbose	Set verbose messages