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Procedure documentation Monitoring Virtual Memory Usage (Informix)  Locate the document in its SAP Library structure

Use

You can use the SAP/Informix database monitor to monitor Informix virtual memory usage. Informix uses almost no malloc memory. Almost all memory used is shared memory. This means that Informix can sometimes run into operating system limits.

For example, on HP-UX 10.25 the maximum amount of shared memory per process is 2.75 GB. The data buffers, dictionary cache, administrative memory, and especially all session-specific memory must fit within this limit. Customers with large installations might have problems remaining within the limit.

Note

Reducing shared memory reduces performance and can even increase the possibility of deadlocks. Reduce it only if you are close to the operating system limit for the maximum amount of shared memory.

For up-to-date recommendations, see SAP Notes 38207 and 41360.

Procedure

  1. Choose Tools ® CCMS ® Control/Monitoring ® Performance Menu ® Database ® Activity ® Detail Analysis Menu ® Shared Memory.

    2. This brings you to the memory monitor where you can view and, if necessary, optimize session pools.

  2. Choose Pools or use the Informix command, onstat -g mem .

    3. Here you can see a list of all pools with their used, free and total memory requirements (that is, used amount, free amount, total amount). You can recognize the session pools by their session id, given in the pool name column.

  3. Look at the column total amount for the size, given in bytes. Session pools are normally smaller than 5 MB.
  4. Intervene in the case of larger session pools. See SAP Note 38307 for a detailed description of what to do.