About Oracle Database server Swap What is the recommended value for this setting

1, the role of swap

Both Systems management and DBAs know that there is a swap partition on both Linux and UNIX systems, which is an example of virtual memory on a Windows system.

When the system's physical memory is not enough, it is necessary to release some of the space in physical memory, temporarily transfer to swap, for the currently running program to provide physical memory space, when the program needs to re-access the data transferred to the swap space, and then recover from the swap to physical memory. Since then work principle does not look out, swap to have, but try not to use, use will occur memory exchange, inevitably affect system performance.

2. Swap Setup Issues

Experienced system administrators and DBAs often give the system a moderate size swap size, but in actual production systems, there are often some, because the swap is set too small to cause the physical memory, swap all exhausted, resulting in the condition of the down machine There is also a case where the swap setting is too big to waste the necessary storage space, and it is important to refer to Oracle's official recommendations.

3. Oracle's official proposed swap setting standard

For an operating system running Oracle database, Oracle has a set size recommendation, as an example of the recommended size extracted from Oracle 12C R1 official Documentation:

4.3.4 Server Memory Minimum Requirements Ensure that your system meets the following memory requirements: Minimum : 1 GB of RAM Recommended : 2 GB of RAM or more Table 4-3 describes the relationship between the installed RAM and the configured swap space recommendation: Table 4-3 Swap Space requirement for Linux Ram Swap Space Between 1 GB and 2 GB 1.5 times the size of the RAM Between 2 GB and GB Equal to the size of the RAM More than GB + GB

(1) Oracle requires a minimum of 1GB RAM, recommended 2GB or greater

(2) Swap vs. RAM size configuration Relationship

1), Ram is 1-2GB, swap size is recommended for 1.5 times times the size of RAM

2), when RAM is 2-16GB, swap size is recommended equal to RAM size

3), Ram greater than 16GB, swap size recommended 16GB

4, large memory environment swap size configuration recommendations

Due to the rapid decline in memory prices, the current production system server memory 256GB, 512GB is no surprise, the author recommends 16-64gb physical memory, swap and physical memory "equivalent" size, larger than 64GB of memory, the recommended general configuration is half the size of physical memory, The specific size can be judged by experience based on business characteristics. Constant observation of swap usage during production can adjust swap size appropriately.

This article Li Junjie (Network Name: casing), engaged in "system architecture, operating systems, storage devices, databases, middleware, applications" six levels of systematic performance optimization work

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About Oracle Database server Swap What is the recommended value for this setting