OpenTP1 Version 7 Operation

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4.6.10 Setting the number of cache blocks for a DAM file

The DAM service stores the block data of the DAM file it reads in the DAM service-exclusive shared memory. When there are multiple reference requests for the same block, the DAM service uses the data in the memory to reduce the number of file I/O operations. In the shared memory, several pieces of block data are chain managed for each DAM file. An area in the DAM service-exclusive shared memory storing block data is called a cache block.

When you use the damchdef command, you can set the maximum number of cache blocks a DAM file can manage (threshold). By setting a threshold, you can effectively use memory resources since cache blocks are reused.

Determine a threshold for the number of cache blocks as follows.

To determine a threshold:

  1. Execute the damchinf command to acquire the cache block information.
    An example output of executing the damchinf command is as follows:
    CleanUP Count:1  Next CleanUP FILE-No:1  Using Rate:80%
      FileNo  FileName  BlkLen  BlkNum  CchBlkNum  PreservNum  LimitNum   ReUse
           1  damfile1     504   10000       7900           0        -1   Exist
           0  damfile0     504   10000        100           0        -1   Exist
           2  damfile2     504   10000          0           0        -1    None
  2. Choose a threshold value based on the type of UAP access.
    • If the UAP will access damfile1 very seldom
      Only 20% of the cache block area can be allocated to damfile0 and damfile2. Since the UAP will hardly access damfile1, the cache block area for the 7,900 cache blocks that are connected to the cache block chain for damfile1 will remain secured. Specify a small value as the threshold for damfile1 to decrease the secured cache block area and increase the cache block area to be allocated to damfile0 and damfile2.
      Since many cache blocks are connected to the cache block chain for damfile1, clean-up processing will be performed if the cache block area becomes insufficient. Since the output result indicates that the clean-up target is 1, that means that the cache block chain for damfile1 is the target of clean-up. In this case, release processing will start for these 7,900 cache blocks and system performance will degrade significantly. To prevent this degradation, you should specify a threshold for damfile1.
    • When the UAP accesses damfile1 frequently
      When the UAP accesses damfile1 frequently, the cache block chain for damfile1 is frequently searched. By specifying a threshold, you can shorten the cache block chain, reducing the chain search time. However, if the threshold is too small, the cache efficiency decreases, degrading performance. Determine an optimum value by testing several thresholds.
    • When the UAP accesses all DAM files uniformly
      When the UAP accesses all DAM files uniformly, the cache block areas allocated to each DAM file should be the same. By setting the same value as the threshold for each DAM file, the cache block area used by each DAM file will be the same.