#include <db_cxx.h> int DbMpoolFile::open(const char *file, u_int32_t flags, int mode, size_t pagesize);
The DbMpoolFile::open() method opens a file in the in-memory cache.
The DbMpoolFile::open()
method either returns a non-zero error value or throws an
exception that encapsulates a non-zero error value on
failure, and returns 0 on success.
The file parameter is the name of the file to be opened. If file is NULL, a private temporary file is created that cannot be shared with any other process (although it may be shared with other threads of control in the same process).
When using a Unicode build on Windows (the default), the file argument will be interpreted as a UTF-8 string, which is equivalent to ASCII for Latin characters.
The flags parameter must be set to zero or by bitwise inclusively OR'ing together one or more of the following values:
Create any underlying files, as necessary. If the database do not already exist
and the DB_CREATE flag is not specified, the
call will fail.
If set and supported by the system, turn off system buffering of the file to avoid double caching.
Open the file with support for multiversion concurrency control. Calls to DbMpoolFile::get() with dirty pages will cause copies to be made in the cache.
Always copy this file into the local cache instead of potentially mapping it into process memory (see the DbEnv::set_mp_mmapsize() method for further information).
Attempts to open files which are not a multiple of the page size in length will fail, by default. If the DB_ODDFILESIZE flag is set, any partial page at the end of the file will be ignored and the open will proceed.
Open any underlying files for reading only. Any attempt to modify the file using the memory pool (cache) functions will fail, regardless of the actual permissions of the file.
On Windows systems, the mode parameter is ignored.
On UNIX systems or in IEEE/ANSI Std 1003.1 (POSIX) environments, files
created by DbMpoolFile::open() are created with mode
mode (as described in chmod(2)) and modified by the process' umask
value at the time of creation (see umask(2)). Created files are owned by the
process owner; the group ownership of created files is based on the system
and directory defaults, and is not further specified by Berkeley DB. System
shared memory segments created by DbMpoolFile::open() are
created with mode mode, unmodified by the
process' umask value. If mode is 0,
DbMpoolFile::open() will use a default mode of readable
and writable by both owner and group.
The DbMpoolFile::open()
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 file has already been entered into the cache, and the pagesize value is not the same as when the file was entered into the cache, or the length of the file is not zero or a multiple of the pagesize; the DB_RDONLY flag was specified for an in-memory cache; or if an invalid flag value or parameter was specified.