#include <db_cxx.h>
extern "C" {
    typedef u_int32_t (*h_hash_fcn_type)
	(DB *, const void *bytes, u_int32_t length);
Db::set_h_hash(h_hash_fcn_type h_hash_fcn);

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 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 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 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 Db::open() was called; or if an invalid flag value or parameter was specified.



See Also

Database and Related Methods