Administering Oracle Database on AIXThis appendix contains information about administering Oracle Database on AIX. It includes the following topics: A. Memory and Paging. Memory contention occurs when processes require more memory than is available. To cope with the shortage, the system pages programs and data between memory and disks. This section contains the following topics: A. Controlling Buffer- Cache Paging Activity.
Excessive paging activity decreases performance substantially. This can become a problem with database files created on journaled file systems (JFS and JFS2). In this situation, a large number of SGA data buffers may also have analogous file system buffers containing the most frequently referenced data. The behavior of the AIX file buffer cache manager can have a significant impact on performance.
It can cause an I/O bottleneck, resulting in lower overall system throughput. It is possible to tune buffer- cache paging activity, but you must do it carefully and infrequently. Use the /usr/sbin/vmocommand to tune the AIX system parameters in the following table.
Parameter. Descriptionminfree. The minimum free- list size. If the free- list space in the buffer falls below this size, then the system uses page stealing to replenish the free list. The maximum free- list size. If the free- list space in the buffer exceeds this size, then the system stops using page stealing to replenish the free list. The minimum number of permanent buffer pages for file I/O. The maximum number of permanent buffer pages for file I/O.
See Also: AIX 5. L Performance Management Guide for more information about AIX system parameters. A. 1. 2 Tuning the AIX File Buffer Cache. The purpose of the AIX file buffer cache is to reduce disk access frequency when journaled file systems are used. If this cache is too small, then disk usage increases and potentially saturates one or more disks. If the cache is too large, then memory is wasted. You can configure the AIX file buffer cache by adjusting the minperm and maxperm parameters. In general, if the buffer hit ratio is low (less than 9.
If maintaining a high buffer hit ratio is not critical, then decreasing the minperm parameter value increases the physical memory available. Refer to the AIX documentation for more information about increasing the size of the AIX file buffer cache.
The performance gain cannot be quantified easily, because it depends on the degree of multiprogramming and the I/O characteristics of the workload. Tuning the minperm and maxperm Parameters. AIX provides a mechanism for you to loosely control the ratio of page frames used for files rather than those used for computational (working or program text) segments by adjusting the minperm and maxperm values according to the following guidelines: If the percentage of real memory occupied by file pages falls below the minperm value, then the virtual memory manager (VMM) page- replacement algorithm takes both file and computational pages, regardless of repage rates. If the percentage of real memory occupied by file pages rises above the maxperm value, then the VMM page- replacement algorithm takes both file and computational pages.
If the percentage of real memory occupied by file pages is between the minperm and maxperm parameter values, then the VMM normally takes only file pages. However, if the repaging rate for file pages is higher than the repaging rate for computational pages, then the computational pages are taken as well. Use the following algorithm to calculate the default values: minperm (in pages) = ((number of page frames)- 1. Use the following command to change the value of the minperm parameter to 5 percent of the total number of page frames, and the value of the maxperm parameter to 2.
The default values are 2. To optimize for quick response when opening new database connections, adjust the minfree parameter to maintain enough free pages in the system to load the application into memory without adding additional pages to the free list. To determine the real memory size (resident set size, working set) of a process, use the following command.
Set the minfree parameter to this value or to 8 frames, whichever is larger. If the database files are on raw devices, or if you are using Direct I/O, then you can set the minperm and maxperm parameters to low values. For example, 5 percent and 2. This is because the AIX file buffer cache is not used either for raw devices or for Direct I/O. The memory may be better used for other purposes, such as for the Oracle System Global Area. A. 1. 3 Allocating Sufficient Paging Space.
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Inadequate paging space (swap space) usually causes the system to stop responding or show very slow response times. On AIX, you can dynamically add paging space on raw disk partitions. The amount of paging space you should configure depends on the amount of physical memory present and the paging space requirements of your applications. Use the lsps command to monitor paging space use and the vmstat command to monitor system paging activities. To increase the paging space, use the smit pgsp command.
Don't Remove Those Log Files! -- Zero Them Out. Here's a technique I use periodically to empty the log files. I simply could remove the file but then I would have to recreate the file and then reset the attributes. A Administering Oracle Database on AIX. The system uses swap space only if it runs out of real memory. the first Oracle block on a file system is always at offset zero.
If paging space is preallocated, then Oracle recommends that you set the paging space to a value larger than the amount of RAM. But on AIX, paging space is not allocated until required. The system uses swap space only if it runs out of real memory. If the memory is sized correctly, then there is no paging and the page space can be small. Workloads where the demand for pages does not fluctuate significantly perform well with a small paging space. Workloads likely to have peak periods of increased paging require enough paging space to handle the peak number of pages.
As a general rule, an initial setting for the paging space is half the size of RAM plus 4 GB, with an upper limit of 3. GB. Monitor the paging space use with the lsps - a command, and increase or decrease the paging space size accordingly. The metric %Used in the output of lsps - a is typically less than 2. A properly sized deployment requires very little paging space and an excessive amount of swapping is an indication that the RAM on the system may be undersized.
Caution. Do not undersize the paging space. If you do, then the system terminates active processes when it runs out of space. However, oversizing the paging space has little or no negative impact. A. 1. 4 Controlling Paging. Constant and excessive paging indicates that the real memory is over- committed.
In general, you should: Avoid constant paging unless the system is equipped with very fast expanded storage that makes paging between memory and expanded storage much faster than Oracle Database can read and write data between the SGA and disks. Allocate limited memory resource to where it is most beneficial to system performance. It is sometimes a recursive process of balancing the memory resource requirements and trade- offs. If memory is not adequate, then build a prioritized list of memory- requiring processes and elements of the system. Assign memory to where the performance gains are the greatest. A prioritized list may look like the following: OS and RDBMS kernels.
User and application processes. Redo log buffer. PGAs and shared pool. Database block buffer caches.
For example, suppose you query Oracle Database dynamic performance tables and views and find that both the shared pool and database buffer cache require more memory. Then, assigning the limited spare memory to the shared pool may be more beneficial than assigning it to the database block buffer caches. The following AIX commands provide paging status and statistics: vmstat - svmstatinterval[repeats]sar - rinterval[repeats]A.
Setting the Database Block Size. You can configure Oracle Database block size for better I/O throughput. On AIX, you can set the value of the DB_BLOCK_SIZE initialization parameter to between 2 KB and 3. KB, with a default of 4 KB. If Oracle Database is installed on a journaled file system, then the block size should be a multiple of the file system block size (4 KB on JFS, 1. K to 1 MB on GPFS). For databases on raw partitions, Oracle Database block size is a multiple of the operating system physical block size (5.
AIX). Oracle recommends smaller Oracle Database block sizes (2 KB or 4 KB) for online transaction processing (OLTP) or mixed workload environments and larger block sizes (8 KB, 1. KB, or 3. 2 KB) for decision support system (DSS) workload environments. A. 1. 6 Tuning the Log Archive Buffers. By increasing the LOG_BUFFER size, you may be able to improve the speed of archiving the database, particularly if transactions are long or numerous.
Monitor the log file I/O activity and system throughput to determine the optimum LOG_BUFFER size. Tune the LOG_BUFFER parameter carefully to ensure that the overall performance of normal database activity does not degrade. Note. The LOG_ARCHIVE_BUFFER_SIZE parameter was obsoleted with Oracle. Database. A. 1. 7 I/O Buffers and SQL*Loader.
For high- speed data loading, such as using the SQL*Loader direct path option in addition to loading data in parallel, the CPU spends most of its time waiting for I/O to complete. By increasing the number of buffers, you can maximize CPU usage, and by doing this, increase overall throughput. The number of buffers (set by the SQL*Loader BUFFERS parameter) you choose depends on the amount of available memory and how much you want to maximize CPU usage. The performance gains depend on CPU usage and the degree of parallelism that you use when loading data.
See Also: Oracle Database Utilities for information about adjusting the file processing options string for the BUFFERS parameter and for information about the SQL*Loader utility. BUFFER Parameter for the Import Utility. The BUFFER parameter for the Import utility should be set to a large value to optimize the performance of high- speed networks when they are used. For example, if you use the IBM RS/6. Scalable POWERparallel Systems (SP) switch, then you should set the BUFFER parameter to a value of at least 1 MB. A. 2 Disk I/O Issues.
Command to reduce a file size to ZEROMark this reply as the best answer?(Choose carefully, this can't be changed)Please find below command to make a file zero with out renaming it. Solaris System Engineer. TDCA Roshan Kabul , Afghanistan" id="ctl.
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