Christian Bilien’s Oracle performance and tuning blog

Memory partitioning strategy: avoiding design traps on high end HP-UX systems. CLM and ILM (2/2)

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CLM and ILM

As seen in the first post on this topic , since HP-UXiv2, and only when cells are dual-core capable (PA-RISC or Itanium 2), it is possible to identify memory on a cell or across an nPar as noninterleaved. This is called Cell-Local Memory, or CLM. CLM can be configured as a quantity or percentage of an individual cell’s memory, or a quantity or percentage of the memory across the entire nPar. Interleaved memory (ILM) is used when a portion of memory is taken from cells of the system and is mixed together in a round robin fashion. With processors on various cells accessing interleaved memory the average access time will be uniform. In 11i v1 all memory is designated as ILM.

The designation of memory as ILM vs. CLM is done at the nPar level (parcreate or parmodify). You can then allocate it to one or more of your vPars (vparcreate or vparmodify).

Cell local memory (CLM) can still be accessed by any processor, but processors on the same cell will have the lowest access latency. Access by processors in other cells will have higher latencies. It is always better to use ILM than accessing CLM configured in another cell.Note that CLM can be used to handle the case when there is an uneven amount of memory in the cells: the delta would be configured as CLM.

Psets

CLM and Processor Sets (Psets) can be used together to avoid the inconsistencies of ccNUMA almost entirely. In this context, locality domain (ldom) is defined as the CPUs and memory required to run a thread. A Pset is a logical grouping of CPUs, a CPU partition so to speak. Oracle processes bound to a given Pset get thread run time only on the CPUs assigned to the given Pset. ccNUMA is eliminated because the data and CPUs are on the same cell or ldom.

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