Redirecting clients with application code

If you use the DBPATH environment variable or connectivity information to redirect connections, you can include in your clients a routine that handles errors when clients encounter a cluster failure. The routine can call another function that contains a loop that tries repeatedly to connect to the other database server in the cluster. This routine redirects clients without requiring the user to exit the application and restart it.

The following example shows an example of a function in a client application using the DBPATH redirection mechanism that loops as it attempts to reconnect. After it establishes a connection, it also tests the type of the database server to make sure it is not a secondary database server. If the database server is still a secondary type, it calls another function to alert the user (or database server administrator) that the database server cannot accept updates.

/* The routine assumes that the INFORMIXSERVER environment
 * variable is set to the database server that the client 
 * normally uses and that the DBPATH environment variable 
 * is set to the other database server in the pair.
 */

#define SLEEPTIME 15
#define MAXTRIES 10

main()
{
   int connected = 0;
   int tries;
   for (tries = 0;tries < MAXTRIES && connected == 0;tries++)
   {
      EXEC SQL CONNECT TO "superstores";
      if (strcmp(SQLSTATE,"00000"))
      {
         if (sqlca.sqlwarn.sqlwarn6 != 'W')
         {
            notify_admin();
            if (tries < MAXTRIES - 1)
               sleep(SLEEPTIME);
            }
         else connected =1;
         }
      }
   return ((tries == MAXTRIES)? -1:0);
   }

This example assumes the DBPATH redirection mechanism and uses a form of the CONNECT statement that supports the DBPATH redirection method. If you used the connectivity information to redirect, you might have a different connection statement, as follows:

EXEC SQL CONNECT TO "superstores@cliff_ol";

In this example, superstores@cliff_ol is a database on a database server that the client computer recognizes. For redirection to occur, the administrator must change the connectivity information to make that name refer to a different database server. You might be required to adjust the amount of time that the client waits before it tries to connect or the number of tries that the function makes. Provide enough time for an administrative action on the database server (to change the connectivity information or change the type of the secondary database server to standard).