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| Swappiness & Net Mem |
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| bobbee |
 Posted: Tue Nov 11, 2025 3:46 am Post subject: Swappiness & Net Mem |
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Knight
Joined: 20 Sep 2001
Posts: 542
Location: Tampa
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Are there recommended settings for Swappiness & Net Mem for MQ.
Swappiness
- REL 8 default is 60
- REL 8 also really started pushing cgroups, so it?s no longer enough to just set swappiness
- RedHat recommends 60 because SSD?s have become blazingly fast
- SSD speed isn?t our issue though, any data written to disk is synchronously replicated which kills us for SWAP.
Net mem
- Using the default net memory settings means that max and default are the same
- This severely limits TCP window scaling (typically to 65k max)
- Increasing the max allows the window to grow as needed to fit the data flow
- Small windows limit how much data can be received before the sender needs to stop and wait for the other side to catch up. |
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| fjb_saper |
| Posted: Sat Nov 15, 2025 10:33 pm Post subject: Re: Swappiness & Net Mem |
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Grand High Poobah
Joined: 18 Nov 2003
Posts: 20769
Location: LI,NY
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| bobbee wrote: |
Are there recommended settings for Swappiness & Net Mem for MQ.
Swappiness
- REL 8 default is 60
- REL 8 also really started pushing cgroups, so it?s no longer enough to just set swappiness
- RedHat recommends 60 because SSD?s have become blazingly fast
- SSD speed isn?t our issue though, any data written to disk is synchronously replicated which kills us for SWAP.
Net mem
- Using the default net memory settings means that max and default are the same
- This severely limits TCP window scaling (typically to 65k max)
- Increasing the max allows the window to grow as needed to fit the data flow
- Small windows limit how much data can be received before the sender needs to stop and wait for the other side to catch up. |
Hi Bobee,
Don't know about swappiness, as I expect this to talk about swap space size and use, and did not see anything int the MQ Doc about that. Although common wisdom would want you to stay out of disk/memory swapping
About memory, there are special settings in Unix that you are supposed to follow and that are specified in the manual. You can verify them by running mqconfig...
Hope it helps 
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