# DB->key_range

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    #include <db.h>

    int
    DB->key_range(DB *db, DB_TXN *txnid,
    	DBT *key, DB_KEY_RANGE *key_range, u_int32_t flags);

# Description

The DB->key_range function returns an estimate of the proportion of keys that are less than, equal to and greater than the specified key. The underlying database must be of type Btree.

The information is returned in the key_range argument, which contains three elements of type double, less, equal and greater. Values are in the range of 0 to 1, e.g., if the field less is 0.05, that indicates that 5% of the keys in the database are less than the key argument. The value for equal will be zero if there is no matching key and non-zero otherwise.

If the file is being accessed under transaction protection, the txnid parameter is a transaction ID returned from txn_begin, otherwise, NULL. The DB->key_range function does not retain the locks it acquires for the life of the transaction, so estimates may not be repeatable.

The flags parameter is currently unused, and must be set to 0.

The DB->key_range function returns a non-zero error value on failure and 0 on success.

# Errors

The DB->key_range function may fail and return a non-zero error for the following conditions:

DB_LOCK_DEADLOCK
  The operation was selected to resolve a deadlock.

EINVAL
  An invalid flag value or parameter was specified.

  The underlying database was not of type Btree.

The DB->key_range function 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->key_range function may fail and return DB_RUNRECOVERY, in which case all subsequent Berkeley DB calls will fail in the same way.

# See Also

db_create, DB->close, DB->cursor, DB->del, DB->err, DB->fd, DB->get, DB->get_byteswapped, DB->get_type, DB->join, DB->key_range, DB->open, DB->put, DB->remove, 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_flags, DB->set_h_ffactor, DB->set_h_hash, DB->set_h_nelem, DB->set_lorder, DB->set_malloc, DB->set_pagesize, DB->set_paniccall, DB->set_q_extentsize, DB->set_realloc, DB->set_re_delim, DB->set_re_len, DB->set_re_pad, DB->set_re_source, DB->stat, DB->sync, DB->upgrade and DB->verify.`

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