int DB->set_h_nelem(DB *db, u_int32_t h_nelem);
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 returns a non-zero error value on failure and 0 on success.
The DB->set_h_nelem method may fail and return a non-zero error for the following conditions:
Called after DB->open was called.
The DB->set_h_nelem method may fail and return a non-zero error for errors specified for other Berkeley DB and C library or system functions. If a catastrophic error has occurred, the DB->set_h_nelem method may fail and return DB_RUNRECOVERY, in which case all subsequent Berkeley DB calls will fail in the same way.
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