The behaviour of these functions is affected by settings in php.ini.
| Name | Default | Changeable | Changelog | 
|---|---|---|---|
| mysql.allow_local_infile | "1" | PHP_INI_SYSTEM | |
| mysql.allow_persistent | "1" | PHP_INI_SYSTEM | |
| mysql.max_persistent | "-1" | PHP_INI_SYSTEM | |
| mysql.max_links | "-1" | PHP_INI_SYSTEM | |
| mysql.trace_mode | "0" | PHP_INI_ALL | Available since PHP 4.3.0. | 
| mysql.default_port | NULL | PHP_INI_ALL | |
| mysql.default_socket | NULL | PHP_INI_ALL | Available since PHP 4.0.1. | 
| mysql.default_host | NULL | PHP_INI_ALL | |
| mysql.default_user | NULL | PHP_INI_ALL | |
| mysql.default_password | NULL | PHP_INI_ALL | |
| mysql.connect_timeout | "60" | PHP_INI_ALL | PHP_INI_SYSTEM in PHP <= 4.3.2. Available since PHP 4.3.0. | 
Here's a short explanation of the configuration directives.
mysql.allow_local_infile
    integer
   Allow accessing, from PHP's perspective, local files with LOAD DATA statements
mysql.allow_persistent
    boolean
   Whether to allow persistent connections to MySQL.
mysql.max_persistent
    integer
   The maximum number of persistent MySQL connections per process.
mysql.max_links
    integer
   The maximum number of MySQL connections per process, including persistent connections.
mysql.trace_mode
    boolean
   Trace mode. When mysql.trace_mode is enabled, warnings for table/index scans, non free result sets, and SQL-Errors will be displayed. (Introduced in PHP 4.3.0)
mysql.default_port
    string
   
     The default TCP port number to use when connecting to
     the database server if no other port is specified. If
     no default is specified, the port will be obtained
     from the MYSQL_TCP_PORT environment
     variable, the mysql-tcp entry in
     /etc/services or the compile-time
     MYSQL_PORT constant, in that order. Win32
     will only use the MYSQL_PORT constant.
    
mysql.default_socket
    string
   The default socket name to use when connecting to a local database server if no other socket name is specified.
mysql.default_host
    string
   The default server host to use when connecting to the database server if no other host is specified. Doesn't apply in SQL safe mode.
mysql.default_user
    string
   The default user name to use when connecting to the database server if no other name is specified. Doesn't apply in SQL safe mode.
mysql.default_password
    string
   The default password to use when connecting to the database server if no other password is specified. Doesn't apply in SQL safe mode.
mysql.connect_timeout
    integer
   Connect timeout in seconds. On Linux this timeout is also used for waiting for the first answer from the server.