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Berkeley DB: DB->set_h_hash
DB->set_h_hash
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#include <db.h>
int
DB->set_h_hash(DB *db,
u_int32_t (*h_hash_fcn)(DB *, const void *bytes, u_int32_t length));
Description: DB->set_h_hash
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.
Parameters
- h_hash_fcn
- 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).
Errors
The DB->set_h_hash method
may fail and return one of the following non-zero errors:
- EINVAL
- If the method was called after DB->open was called; the
specified hash function differs from the hash function with which the
database was created; or if an
invalid flag value or parameter was specified.
Class
DB
See Also
Databases and Related Methods
Copyright (c) 1996-2004 Sleepycat Software, Inc. - All rights reserved.
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