#include <db.h>
int
DB->set_h_hash(DB *db,
u_int32_t (*h_hash_fcn)(DB *dbp, const void *bytes,
u_int32_t length));
Set a user-defined hash function; if no hash function is specified, a default hash function is used. Because no hash function performs equally well on all possible data, the user may find that the built-in hash function performs poorly with a particular data set.
The DB->set_h_hash() method configures operations performed using the
specified DB handle, not
all operations performed on the underlying database.
The DB->set_h_hash() method may not be called after the
DB->open() method is called. If
the database already exists when DB->open()
is called, the information specified to DB->set_h_hash() must be the same as that
historically used to create the database or corruption can occur.
The DB->set_h_hash()
method returns a non-zero error value on failure and 0 on success.
The h_hash_fcn parameter is the application-specified hash function.
Application-specified hash functions take a pointer to a byte string and a length as parameters, and return a value of type u_int32_t. The hash function must handle any key values used by the application (possibly including zero-length keys).
The DB->set_h_hash()
method may fail and return one of the following non-zero errors:
If the method was called after DB->open() was called; or if an invalid flag value or parameter was specified.