Typically when working with DB2, a problem is manifested by an error message. The error message may be reported immediately to the user, or it may be stored in some diagnostic file like the administration notification log or the db2diag.log (these diagnostic files are discussed in section 17.4, DB2 First Failure Data Capture).
Figures 17.2 and 17.3 show examples of DB2 reporting problems immediately after executing an operation. In Figure 17.2, after clicking on the instance MYINST in the object tree of the Control Center, getting the DB2 message SQL1032N indicates that this instance has not started.
In Figure 17.3, after entering the SQL statement select from employee in the CLP, getting the error SQL0104N indicates there is a syntax error in the statement (column names have not been specified).
Some problems may not report an error message. For example, if the DB2 instance hangs or the response time is very slow, you may need to run traces (see section 17.7, The DB2 Trace Facility).