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1. A caller never allocates the ComDiagsArea, but instead passes a reference to a pointer to the callee. The caller initializes the pointer to NULL. When an error/warning is raised the callee needs to allocate ComDiagsArea (if not already allocated) and populate it. Then the caller moves it to the objects of step 3 and destroys the ComDiagsArea allocated in the callee.
2. In case of a process hop, the ComDiagsArea is shipped from the child only when there is an error or warning via IPC mechanism.
3. While switching back from "META" CmpContext to user CmpContext, the errors/warnings from the META CmpContext are copied to the user CmpContext.
4. Applications such as sqlci and mxosrvr should attempt to obtain the diagnostics info based on the return code of a CLI call. When the return code is 100, get the number of error condition via less expensive call SQL_EXEC_GetDiagnosticsStmtInfo2. When this call returns two or more conditions, then there are warnings other than 100.
5. Use mark/rewind and other methods of ComDiagsArea to manipulate it rather than creating and copying it.

In the Executor, there is a macro, ExRaiseSqlError, that should be used. It takes care of the details of allocating a ComDiagsArea object if needed, and inserting the diagnostic into ComDiagsArea.

Code reviewers should monitor code changes involving ComDiagsArea to make sure these practices are followed.

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