[DOCS-11746] Wrong swappiness configuration recommendation Created: 29/May/18 Updated: 30/Oct/23 |
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| Status: | Closed |
| Project: | Documentation |
| Component/s: | manual, Server |
| Affects Version/s: | None |
| Fix Version/s: | Server_Docs_20231030 |
| Type: | Bug | Priority: | Major - P3 |
| Reporter: | Ricardo Lorenzo | Assignee: | Ravind Kumar (Inactive) |
| Resolution: | Won't Do | Votes: | 1 |
| Labels: | None | ||
| Remaining Estimate: | Not Specified | ||
| Time Spent: | Not Specified | ||
| Original Estimate: | Not Specified | ||
| Issue Links: |
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| Participants: | |||||||||
| Days since reply: | 1 year, 14 weeks, 2 days ago | ||||||||
| Epic Link: | DOCSP-1769 | ||||||||
| Story Points: | 0.1 | ||||||||
| Description |
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I have found today that the official recommendation is to set vm.swappiness to 1. I do believe this is a serious misunderstanding of the purpose of the swap space. Apparently, the documentation was worse (set to 0) as I can see on From the official Linux documentation you can read the following:
The swap usage is not a problem by itself. The only problem which may affect performance is if the operating system is actively paging in and out which can be tracked using vmstat. You can find many articles in relation to this subject: https://chrisdown.name/2018/01/02/in-defence-of-swap.html In the previous documentation ticket, the value of 10 was suggested which is better than 1. However, I would not recommend changing anything unless you really know what you are doing and you have the tools to observe the behavior and the impact.
ScopeBased on internal discussions, we're going to remove this recommendation until performance testing completes and we have more data to back any recommendations in one direction or another. We will backport this removal to 3.6. |
| Comments |
| Comment by Education Bot [ 31/Oct/22 ] |
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Hello! This ticket has been closed due to inactivity. If you believe this ticket is still important, please reopen it and leave a comment to explain why. Thank you! |
| Comment by Henrik Ingo (Inactive) [ 24/Jan/19 ] |
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I didn't want to suggest more than one alternative, but for the record, I am not against removing this recommendation entirely. |
| Comment by Bruce Lucas (Inactive) [ 10/Jan/19 ] |
Not to mention if mongod itself uses much more memory than expected, and there are a number of known reasons this can happen. However it seems debatable to me whether it's better to start paging and run really slowly for a long time, or fall over and restart quickly in this scenario. |
| Comment by Henrik Ingo (Inactive) [ 09/Jan/19 ] |
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I believe Atlas tested Ricardo's recommendation on the smaller instances, but "felt" that if anything, it made things worse. Cailin said this in an email once. I'm intentionally not pinging her, as she probably has more important things to focus on today. But someone could ask Cloud team about this at a later time. |