Re: Linux kernel vm settings

Hi Roberto, I don't have specific recommendations, but i can share my experience with the administration of the scilens cluster. As far as i can remember, i never received requests to change anything related to the vm.overcommit settings. I did receive questions about the swappiness. I never changed the default that fedora uses, but some people wanted to change the value to check some specific use case, including MonetDB, if i remember correctly. But i don't think that it generally matters a lot, i mean, i never heard about that making a big difference. So unless some vendor has a specific reason to suggest some specific version, i would keep the default. We also kept the amount of swapspace very low, intentionally. In the situation you describe, when MonetDB is the "only" program running, it can use all of the available memory. If the application needs more memory and starts to swap, the performance drop significantly. And likely never finishes. Because in most cases it is some kind of bug. Having a lot of swap only postpones the inevitable, the system runs out of memory. With a lot of swap, it just takes much longer to crash. Arjen de Rijke ----- Original Message -----

From: "Roberto Cornacchia" To: "Communication channel for MonetDB users" Sent: Thursday, February 25, 2021 6:31:18 PM Subject: Linux kernel vm settings

Hi there,

I looked around but couldn't find any recommendation about kernel vm settings in Linux for MonetDB.

In particular:

- vm.overcommit_memory: 0 (default) : a heuristics decides whether overcommitting is allowed 1: no check, overcommit is always allowed 2: overcommitting is regulated by vm.overcommit_ratio (default = 50%)

Do I understand correctly that using vm.overcommit_memory=1 will only make the OOM kill mserver5 when the total VM available is exhausted?

If that is true, should it be reasonably safe to use on a server that is mainly intended for MonetDB, as long as sufficient disk space is available?

- vm.swappiness Generic recommendations are usually 60 for a desktop and 30 for a server. Oracle recommends 10. Redis recommends 1. Are there studies / recommendations for MonetDB?

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