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Minimizing System Dump File Size When Disk Space Is Insufficient  



In certain system configurations, it might be impossible to preserve the entire contents of memory in a disk file. For instance, a large memory system might not be able to supply enough disk space for a full memory dump. If your system attempts to save all of memory but the dump file is too small to accommodate the entire dump, the System Dump Analyzer utility (SDA) might not be able to analyze the dump.

On VAX systems, insufficient dump space would also prevent the Crash Log Utility Extractor (CLUE) from being able to analyze the dump.

Options for Minimizing System Dump File Size

Use one of the following options to minimize the size of the system dump file when disk space is insufficient:

Understanding the Order of Information in a Selective System Dump discusses the order in which information is written to a selective system dump on Alpha, I64, and VAX systems. Fine-Tuning the Order That Processes Are Written in Selective System Dumps (Alpha and I64) discusses how this order can be fine-tuned on Alpha and I64 systems.

Understanding the Order of Information in a Selective System Dump  

The following lists show the order in which information is written to selective dumps on VAX, Alpha, and I64 systems.

On VAX systems, information is written to selective dumps in the following order:

  1. System page table (SPT)
  2. System space (including process page tables, page frame number (PFN) database, and global page table (GPT) )
  3. Global pages that appear in the working set of any process
  4. Processes resident at the time of the crash:

    1. Current process on crash CPU
    2. Predefined processes (hardcoded into BUGCHECK)
    3. Current processes on other CPUs
    4. Other processes resident at the time of the crash, in order by process index

On Alpha and I64 systems, information is written to selective system dumps in the following order:

  1. Page table (PT) space for shared addresses (S0/S1/S2)
  2. S0/S1 space
  3. S2 space
  4. Any system space pages (P1, S0/S1, S2) that have been replicated for performance reasons, where the contents of the replicated page is different from the original
  5. Memory map pages for Galaxy shared memory regions, if appropriate
  6. Key processes:

    1. Current process on crash CPU
    2. Swapper
    3. Current processes on CPUs that have failed to record their crash state
    4. Current processes on other CPUs
    5. Site-specific priority processes (see next section)
    6. HP-defined priority processes (hardcoded into BUGCHECK):
      MSCPmount

      AUDIT_SERVER

      NETACP

      NET$ACP

      REMACP

      LES$ACP
  7. Any processes in a resource or miscellaneous wait state (for example, RWAST)
  8. Key global pages (those that appear in the working set of any key process)
  9. Other processes (the non-key processes) resident at the time of the crash, in order by process index
  10. Remaining global pages that appear in the working set of any non-key process

Note that on Alpha and I64 systems, processes are dumped in two stages: the page tables for the process first, and then the body of the process.

Usage Notes on Alpha, I64, and VAX Systems

On Alpha, I64, and VAX platforms, no process is dumped twice. For example, on Alpha and I64 systems, if the current process is the Swapper, it is dumped only once.

Similarly, on Alpha and I64 systems, no global page is dumped twice. Therefore, if a page in the working set of a key process is dumped in the "Key global pages" section, it is not dumped again later just because it is also in the working set of a non-key process.

Fine-Tuning the Order That Processes Are Written in Selective System Dumps (Alpha and I64)  

On Alpha and I64 systems, a set of processes, known as key processes, are dumped immediately following PT, S0/S1, and S2, including transition pages that link back to the process. The system manager can designate additional processes to be treated as key processes. These processes have priority over other processes in a dump, thus ensuring that the selected processes are successfully written when the dump file is too small to contain all processes.

How to Perform This Task

To designate the order of processes in a dump, use the SYSMAN DUMP_PRIORITY commands:

You can add new processes and update the in-memory copy of the list at any time the system is running. Therefore, if a process is hung, the system manager can designate the process as a priority process and then force a crash.


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