MySQL :: MySQL 8.0 C API Developer Guide :: 5.4.59 mysql_real_connect_dns_srv() (original) (raw)

5.4.59 mysql_real_connect_dns_srv()

MYSQL *
mysql_real_connect_dns_srv(MYSQL *mysql,
                           const char *dns_srv_name,
                           const char *user,
                           const char *passwd,
                           const char *db,
                           unsigned long client_flag)

Description

mysql_real_connect_dns_srv() is similar tomysql_real_connect(), except that the argument list does not specify the particular host of the MySQL server to connect to. Instead, it names a DNS SRV record that specifies a group of servers. For information about DNS SRV support in MySQL, seeConnecting to the Server Using DNS SRV Records.

The dns_srv_name argument formysql_real_connect_dns_srv() takes the place of the host,port, and unix_socket arguments formysql_real_connect(). Thedns_srv_name argument names a DNS SRV record that determines the candidate hosts to use for establishing a connection to a MySQL server.

The mysql, user,passwd, db, andclient_flag arguments tomysql_real_connect_dns_srv() have the same meanings as formysql_real_connect(). For descriptions of their meanings, seeSection 5.4.58, “mysql_real_connect()”.

Suppose that DNS is configured with this SRV information for the example.com domain:

Name                     TTL   Class   Priority Weight Port Target
_mysql._tcp.example.com. 86400 IN SRV  0        5      3306 host1.example.com
_mysql._tcp.example.com. 86400 IN SRV  0        10     3306 host2.example.com
_mysql._tcp.example.com. 86400 IN SRV  10       5      3306 host3.example.com
_mysql._tcp.example.com. 86400 IN SRV  20       5      3306 host4.example.com

To use that DNS SRV record, pass"_mysql._tcp.example.com" as thedns_srv_name argument tomysql_real_connect_dns_srv(), which then attempts a connection to each server in the group until a successful connection is established. A failure to connect occurs only if a connection cannot be established to any of the servers. The priority and weight values in the DNS SRV record determine the order in which servers should be tried.

mysql_real_connect_dns_srv() attempts to establish TCP connections only.

The client library performs a DNS SRV lookup for each call tomysql_real_connect_dns_srv(). The client library does no caching of lookup results.

Return Values

A MYSQL* connection handler if the connection was successful, NULL if the connection was unsuccessful. For a successful connection, the return value is the same as the value of the first argument.

Example

The following example uses the name of the DNS SRV record shown previously as the source of candidate servers for establishing a connection.

MYSQL mysql;
const char *dns_srv_name = "_mysql._tcp.example.com";

mysql_init(&mysql);
if (!mysql_real_connect_dns_srv(&mysql,dns_srv_name,"user","passwd","database",0))
{
    fprintf(stderr, "Failed to connect to database: Error: %s\n",
          mysql_error(&mysql));
}