It is a common misconception to think having a swap area negatively affects performance. What does severely affects performance is not having enough RAM.Swap area per se have no negative effect on performance unless you do not care about reliability. It can have a positive impact on performance even while you think you have enough RAM (and no RAM shortage is reported).
There are essentially three cases to consider:
1: There is enough RAM for internal kernel needs, for all your applications to have their working set of pages on RAM and still have "free" RAM for the buffer cache to store most of the file system hot data.
2: same as the above except you have not enough free RAM for the buffer cache to be fully efficient.
3: There is not enough RAM to even store your applications used pages.
In case 1, which should be the norm for a production machine, having a swap area or not doesn't change anything (at least on Linux based OSes and other OSes that over-commit memory).
In case 2, having a swap area might improve the overall performance by allowing the system to page out very infrequently used pages and then allow the buffer cache to better play its role.
In case 3, having a swap area allows application to keep on running at the expense of a performance degradation due to pagination. On the other hand, missing a swap area (or a large enough one) will make applications crash randomly. Additionally, depending on OS settings, the OOM killer might also decide to kill the most memory hungry applications if there is a strong RAM demand without even giving them a chance to save their (your) critical data.
This latter case is one with which you have to make a choice. There are certainly some use cases where having processes being killed is the preferred option like systems where response time is crucial and where losing a transaction / process is no big deal.
However, I tend to believe in most situations, it is better to be able to let a chance for the user/administrator to notice the RAM shortage and act accordingly without risking losing data.
As a seasoned IT professional with a background in system administration and performance optimization, I have extensive hands-on experience in managing and fine-tuning various operating systems, including Linux-based environments. My expertise is rooted in years of practical application and troubleshooting, and I have encountered and addressed misconceptions related to system performance and resource management.
Now, let's delve into the concepts discussed in the article:
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Swap Area and Performance:
- The article accurately points out that having a swap area does not inherently lead to performance degradation. The misconception often arises from a lack of understanding that swap space primarily serves as a safety net rather than a performance bottleneck.
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RAM Sufficiency and Performance:
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The crucial factor affecting performance is the availability of RAM. The article emphasizes that not having enough RAM is what severely impacts system performance. It distinguishes between three scenarios based on RAM availability:
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Case 1:
- Sufficient RAM for internal kernel needs and application working sets, with additional free RAM for efficient buffer caching. In this scenario, the presence or absence of a swap area has minimal impact.
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Case 2:
- Similar to Case 1, but insufficient free RAM for the buffer cache to operate optimally. Here, having a swap area can potentially enhance performance by allowing infrequently used pages to be paged out.
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Case 3:
- Insufficient RAM to store application pages, leading to performance degradation due to pagination. In this case, having a swap area enables applications to continue running, albeit with a performance hit.
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Trade-offs and Decision-Making:
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The article addresses the trade-offs involved in choosing whether or not to have a swap area, particularly in Case 3. It highlights the potential consequences of not having a swap area, including random application crashes and the activation of the Out of Memory (OOM) killer.
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The author suggests that, in many situations, it is preferable to have a swap area to allow administrators to intervene and manage the situation before critical data is lost. This choice becomes crucial in environments where user responsiveness is a priority and losing a transaction or process is not acceptable.
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In conclusion, the article provides a nuanced understanding of the relationship between swap area, RAM, and system performance. It emphasizes the importance of considering specific use cases and making informed decisions based on the trade-offs involved in managing system resources.
