# Db::set_h_nelem

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    #include <db_cxx.h>

    int
    Db::set_h_nelem(u_int32_t h_nelem);

# Description

Set an estimate of the final size of the hash table.

In order for the estimate to be used when creating the database, the Db::set_h_ffactor method must also be called. If the estimate or fill factor are not set or are set too low, hash tables will still expand gracefully as keys are entered, although a slight performance degradation may be noticed.

The Db::set_h_nelem method configures a database, not only operations performed using the specified Db handle.

The Db::set_h_nelem interface may not be called after the Db::open interface is called. If the database already exists when Db::open is called, the information specified to Db::set_h_nelem will be ignored.

The Db::set_h_nelem 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_nelem 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_nelem 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_nelem method may fail and either return DB_RUNRECOVERY or throw a DbRunRecoveryException, in which case all subsequent Berkeley DB calls will fail in the same way.

# Class

Db

# See Also

Databases and Related Methods`

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