Technical data

SDA Description
3 Analyzing a Running System
Occasionally, an internal problem hinders system performance but does not
cause a system failure. By allowing you to examine the running system,
SDA provides the means to search for the solution to the problem without
disturbing the operating system. For example, you can use SDA to examine
the stack and memory of a process that is stalled in a scheduler state, such
as a miscellaneous wait (MWAIT) or a suspended (SUSP) state (see OpenVMS
Performance Management).
If your process has change-mode-to-kernel (CMKRNL) privilege, you can invoke
SDA to examine the system. Use the following DCL command:
$ ANALYZE/SYSTEM
SDA then does the following:
1. Attempts to load the system symbol table (SYS$SYSTEM:SYS.STB) and
symbol table SYS$SYSTEM:REQSYSDEF.STB.
2. Executes the contents of any existing SDA initialization file, as it does when
invoked to analyze a crash dump (see Sections 2.3 and 2.4, respectively).
3. Displays its identification message and prompt, as follows:
OpenVMS System analyzer
SDA>
The SDA> prompt indicates that you can use SDA interactively and enter SDA
commands. When analyzing a running system, SDA sets its process context to
that of the process running SDA.
If you are undertaking an analysis of a running system, take the following
considerations into account:
• When used in this mode, SDA does not map the entire system but instead
retrieves only the information it needs to process each individual command.
To update any given display, you must reissue the previous command.
Caution
When using SDA to analyze a running system, use caution in interpreting
its displays. Because system states change frequently, it is possible that
the information SDA displays might be inconsistent with the actual,
volatile state of the system at any given moment.
• Certain SDA commands are illegal in this mode, such as SHOW CPU and
SET CPU. If you use these commands, SDA displays the following error
message:
%SDA-E-CMDNOTVLD, command not valid on the running system
• The SHOW CRASH command, although valid, does not display the contents
of any of the processor’s set of hardware registers. Also, the ‘‘Time of system
crash’’ information refers to the time you entered the ANALYZE/SYSTEM
command.
SDA–11