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The tuned-adm command line tool enables switching between different tuning profiles in Linux. In this best practice, we used the tuned-adm tool to switch to an optimized Linux profile for Oracle.
Overview
The Linux operating system provides a system tuning tool called tuned. This is a profile-based tool that uses a udev device manager. The tuned-adm tool enables the Linux administrator to switch between profiles for the operating system. Pre-defined profiles enable the application of Linux configuration settings in a package that can be downloaded. In this best practice, the Red Hat operating system tuned profile TUNED-PROFILES-ORACLE was downloaded and installed in the Linux operating system. As the result, the following settings were added to the system:
THP is a Linux memory management that reduces the overhead of Translation Lookaside Buffer (TLB) lookups on machines with large amount of memory by using larger memory pages. Oracle databases do not use THP.
Swap space is used by the Linux kernel as virtual memory. The swappiness setting defines how aggressively the kernel will swap memory pages to disk. By changing VM.SWAPPINESS to 1, the kernel is instructed to swap as little as possible to disk and keep more memory pages in RAM.
The DIRTY_BACKGROUND_RATIO is the percentage of memory that contains free and reclaimable pages, that can be filled with dirty pages before the pages are written to disk. Databases can aggressively use the kernel page cache thus lowering the background ratio forces the kernel to flush the dirty pages to disk more frequently.
The DIRTY_RATIO is the percentage of total system memory that contain dirty pages before the pages are written to disk. By setting DIRTY_RATIO to 80 the kernel is instructed to use 80% of total system memory for dirty pages before having to flush the data to disk.
The DIRTY_EXPIRE_CENTISECS define in centisecs, one hundredth of a second, when data is old enough to be written to disk. By setting DIRTY_EXPIRE_CENTISECS to 500, a dirty page can stay in memory for 500 centisecs before it is written to disk.
The DIRTY_WRITEBACK_CENTISECS parameter defines the frequency in which the kernel will check to write dirty pages to disk. In this case, a value of 100 centisecs instructs the kernel to check every 100 centisecs to write dirty pages to disk.
VM.TCP_RMEM_MAX is set to 4194304
The VM.TCP_RMEM_MAX parameter defines the maximum amount of receive socket memory.
In addition to the VM memory settings, this best practice also included network and kernel settings updated by the Oracle tuned profile. The following list describes the network and kernel settings that were updated by the Oracle tuned profile:
Additional resources