Проект OpenNet: MAN hash (3) Библиотечные вызовы (FreeBSD и Linux)

Интерактивная система просмотра системных руководств (man-ов)

hash (3)

hash (1) ( Solaris man: Команды и прикладные программы пользовательского уровня )

hash (1) ( FreeBSD man: Команды и прикладные программы пользовательского уровня )

hash (1) ( Linux man: Команды и прикладные программы пользовательского уровня )

hash (1) ( POSIX man: Команды и прикладные программы пользовательского уровня )

>> hash (3) ( FreeBSD man: Библиотечные вызовы )

hash (3) ( Русские man: Библиотечные вызовы )

hash (3) ( Linux man: Библиотечные вызовы )

hash (9) ( FreeBSD man: Ядро )

Ключ hash обнаружен в базе ключевых слов.

BSD mandoc

NAME



hash

 - hash database access method

SYNOPSIS

#include <sys/types.h>
#include <db.h>

DESCRIPTION

The routine dbopen ();
is the library interface to database files. One of the supported file formats is files. The general description of the database access methods is in dbopen(3), this manual page describes only the specific information.

The data structure is an extensible, dynamic hashing scheme.

The access method specific data structure provided to dbopen ();
is defined in the #include <db.h>
include file as follows:

typedef struct {
        u_int bsize;
        u_int ffactor;
        u_int nelem;
        u_int cachesize;
        u_int32_t (*hash)(const void *, size_t);
        int lorder;
} HASHINFO;

The elements of this structure are as follows:

bsize: The bsize element defines the table bucket size, and is, by default, 256 bytes. It may be preferable to increase the page size for disk-resident tables and tables with large data items.
ffactor: The ffactor element indicates a desired density within the table. It is an approximation of the number of keys allowed to accumulate in any one bucket, determining when the table grows or shrinks. The default value is 8.
nelem: The nelem element is an estimate of the final size of the table. If not set or set too low, tables will expand gracefully as keys are entered, although a slight performance degradation may be noticed. The default value is 1.
cachesize: A suggested maximum size, in bytes, of the memory cache. This value is only advisory, and the access method will allocate more memory rather than fail.
hash: The hash element is a user defined function. Since no function performs equally well on all possible data, the user may find that the built-in function does poorly on a particular data set. User specified functions must take two arguments (a pointer to a byte string and a length) and return a 32-bit quantity to be used as the value.
lorder: The byte order for integers in the stored database metadata. The number should represent the order as an integer; for example, big endian order would be the number 4,321. If lorder is 0 (no order is specified) the current host order is used. If the file already exists, the specified value is ignored and the value specified when the tree was created is used.

If the file already exists (and the O_TRUNC flag is not specified), the values specified for the bsize , ffactor , lorder and nelem arguments are ignored and the values specified when the tree was created are used.

If a function is specified, hash_open ();
will attempt to determine if the function specified is the same as the one with which the database was created, and will fail if it is not.

Backward compatible interfaces to the older dbm and ndbm routines are provided, however these interfaces are not compatible with previous file formats.