The conflict of memory access is now in the process of physical memory of the process exceeds the physical memory of the system, in order to handle this situation, the system exchanges the program and data between memory and hard disk. Controlling a large amount of memory switching operations greatly affects the performance of the system, especially when the database file is created on a file system (JFS and JFS2). In this case, the data that is often accessed, that is, in the SGA, and also exists in the cache of the file. This same data is cached in memory twice, which reduces the efficiency of memory, so that the memory is frequently exchanged, resulting in the system's I / O bottleneck, and reduces the performance of the entire system. Adjusting the files on the AIX in AIX, you can adjust the system file cache through the minperm and maxperm parameters in the VMTune command to control the memory switching operation, the adjustment of the MinPerm and MaxPerm parameters should follow the principles of the following principles:
When the file cache page in memory is below MinPerm, the memory page swap algorithm simultaneously swaps the file cache page and the program page (Computational Pages) When the file cache page in the memory is above the Maxperm, the memory page switched algorithm only swaps the file cache page. When the file cache page in memory is between the MinPerm and Maxperm, the memory page switched algorithm usually only swaps the file cache page, but if the switch page of the file cache is greater than the program page, the program page is also swapped. Default value of MinPerm and MaxPerm parameters minperm = (Number of Memory Page) - 1024) * 0.2maxperm = (Number of Memory Page) - 1024) * 0.8 You can use the following command to set Minperm to 5% memory page, Maxperm is set to 20% memory page. # VMTune -P 5 -P 20 Defaults are 20% and 80%, respectively. In an Oracle database application, Minperm and MaxPerm can be set to 5% and 20%, respectively, so that memory is morely used for Oracle's SGA rather than the system's file cache. Configuring enough switched zones If the switching area is insufficient, the system response speed is slow, and the size of the switching area depends on the size of the system memory and the demand for the application. In AIX, you can dynamically increase the switching zone, or use the LSPS command to view the use of the switching area, and the operation of monitoring the system memory with the VMSTAT monitoring. Usually the size of the switching area needs to be greater than the actual memory of the system, depending on the application's demand for the application. The user needs to monitor the use of the switch area, and the space of the switching area is increased as needed. For running Oracle Application or Oracle Development Tools, you may need a large switching space. Scheduling Memory Demand Priority If the system's memory is insufficient, you need to sort the priority of the process for the process, and the memory is prioritized to get a better system overall performance. The usual order is as follows: 1. AIX and Oracle Core Process 2. Application Process 3. Oracle's Redo Log Buffer4. PGA and Shared Pool 5. Oracle's Data Cache, for example: When you query Oracle's dynamic performance tables Discover the shared pool and data buffer (block buffer cache) need to configure more memory, and the idle memory in your system is limited, then assign idle memory to shared pool ratio assignment There is a better effect to the data cache area. The size of the data block can select the size of the data block in the Oracle database to achieve better performance, and select the DB_BLOCK_SIZE initialization parameters on AIX, select data blocks from 2kb to 32kb, the default value is 4KB. If the data file is on the file system, the size of the Oracle data block should be an inexplicable number of file system data block 4kb. If the data file is on the system bare device, the size of the Oracle data block should be an integer of the system data block 512b. Oracle recommends that 2KB or 4KB data block is used for an application (OLTP) or hybrid application environment for online transactions. For BI Application or Decision Support System (DSS), a larger data block, such as 8kb, 16kb or 32kb. Adjusting the log archive cache Configure a larger cache to increase the speed of the database log archive, but pay attention not to affect the performance of the entire system. Users can add log_archive_buffer_size to 128KB (its default value 4KB), which increases the performance of 0-20% of database archiving operations. Adjusting the size of the SGA For Oracle SGAs, the system's memory management program is changed to the switching area, which is definitely the case where the user is most reluctant to see, which requires a system configuration with sufficient memory.
For a large number of users online, it is recommended to configure a larger SGA zone. The maximum parameters of the SGA affects DB_BLOCK_BUFFERS and Shared_Pool_SIZE. Increase these two parameters depending on the size of the user wants to assign to SGA memory, while increasing the two parameters can also increase the utilization rate of the CPU. The memory configuration of small clamps is an important aspect of Oracle Database performance adjustment. The fundamentally targets are to first avoid the switching operation of the system memory page, and then try to use the data to be used in the system's SGA area. related articles:
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