Using a Debugger

To debug your DataBlade module, use a debugger that can attach to the active server process and access the symbol tables of dynamically loaded shared object files.

debugger - pid

The following sections describe these steps.

Creating a Debugging Version

To debug a shared-object file, you must compile the shared-object file with an option that makes additional symbol-table information available to the debugger. Many C compilers use the -g compiler option to create a debugging version of a shared-object file. For more information on how to compile, see Compiling a C UDR.

Connecting to the Database Server from a Client

To connect to the database server, choose a client tool that allows you to submit ad-hoc queries.

dbaccess database

Loading the Shared-Object File for Debugging

To load the shared-object file, you must execute one of the UDRs within the file. One technique is to execute the UDR itself within DB–Access. For example, if a user-defined function named my_udf( ) resides within the shared-object file, you can use the following SQL statement to execute my_udf( ), which causes the database server to load the shared-object file that contains my_udf( ):

EXECUTE FUNCTION my_udf( );

Another technique for loading the shared-object file is to define a dummy UDR in the shared-object file that you use to load the shared-object file, as follows:

1. Create the dummy UDR in the shared-object file.

   The routine can be as simple as the following example:

   mi_integer load_so( )
   {
      return 0;
   }

   To prevent name conflicts with other shared-object files (or DataBlade modules), you can put a prefix in the routine name.

2. Compile the shared-object file.
3. Register the dummy UDR with the CREATE FUNCTION statement.

   CREATE FUNCTION load_so( )
   RETURNS INTEGER
   WITH (NOT VARIANT)
   EXTERNAL NAME '/usr/lib/udrs/myudrs.so(load_so)'
   LANGUAGE C;

To load the shared-object file, execute the dummy UDR. The following SELECT statement in your client application (or DB–Access) loads the myudrs shared-object file, which contains load_so( ):

SELECT load_so( ) FROM informix.systables WHERE tabid=1;

For more information about loading a shared-object file, see Loading a Shared-Object File.

Identifying the VP Process

To find the virtual processor in which your shared-object file is loaded, execute the onstat utility with the -g glo or -g sch option. Locate the CPU or user-defined virtual processor that you want to debug and record its process identifier (pid) for the next step. For more information on the -g glo and -g sch options of onstat, see Monitoring Virtual Processors.