# Db::set_h_ffactor

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    #include <db_cxx.h>

    int
    Db::set_h_ffactor(u_int32_t h_ffactor);

# Description

Set the desired density within the hash table.

The density is an approximation of the number of keys allowed to accumulate in any one bucket, determining when the hash table grows or shrinks. If you know the average sizes of the keys and data in your data set, setting the fill factor can enhance performance. A reasonable rule computing fill factor is to set it to the following:

>     (pagesize - 32) / (average_key_size + average_data_size + 8)

If no value is specified, the fill factor will be selected dynamically as pages are filled.

The Db::set_h_ffactor interface may be used only to configure Berkeley DB before the Db::open interface is called.

The Db::set_h_ffactor 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.

# Errors

The Db::set_h_ffactor method may fail and throw an exception or return a non-zero error for the following conditions:

EINVAL
  An invalid flag value or parameter was specified.

  Called after Db::open was called.

The Db::set_h_ffactor method may fail and throw an exception or return a non-zero error for errors specified for other Berkeley DB and C library or system methods. If a catastrophic error has occurred, the Db::set_h_ffactor method may fail and either return DB_RUNRECOVERY or throw an exception encapsulating DB_RUNRECOVERY, in which case all subsequent Berkeley DB calls will fail in the same way.

# Class

Db

# See Also

Db::associate, Db::close, Db::cursor, Db::del, Db::err, Db::errx Db::fd, Db::get, Db::pget, Db::get_byteswapped, Db::get_type, Db::join, Db::key_range, Db::open, Db::put, Db::remove, Db::rename, Db::set_alloc, Db::set_append_recno, Db::set_bt_compare, Db::set_bt_minkey, Db::set_bt_prefix, Db::set_cachesize, Db::set_dup_compare, Db::set_errcall, Db::set_errfile, Db::set_errpfx, Db::set_feedback, Db::set_flags, Db::set_h_ffactor, Db::set_h_hash, Db::set_h_nelem, Db::set_lorder, Db::set_pagesize, Db::set_paniccall, Db::set_q_extentsize, Db::set_re_delim, Db::set_re_len, Db::set_re_pad, Db::set_re_source, Db::stat, Db::sync, Db::truncate, Db::upgrade, and Db::verify.`

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