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R80.20 (mlm) log servers swapping

I have experienced a couple R80.20 MDS log servers swapping, this could include log servers as well. The customers have enough RAM, so the file system cache eats up about 60 % of available memory. Still the system swap is increasing slowly. We are using either GA or ongoing take JHF on both systems. The MDS is neither swapping nor using as much cache as the MLM.

Anyone experiencing the same problem?

Check your swap usage with free/top and sar:

 

[Expert@mdlog:0]# free -m
total used free shared buff/cache available
Mem: 15921 5505 271 241 10144 9522
Swap: 8189 526 7663

[Expert@mlm:0]# for safile in $safiles; do sar -S -f "/var/log/sa/$safile" |grep Average|awk '{print $3}'; done
0
6160
28746
58714
27729
...
411624
453370
495278
518524

 

 

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4 Replies
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Re: R80.20 (mlm) log servers swapping

About 10GB of your 16GB of RAM is used for buffering/caching and could be reallocated for code execution if needed, so the system is definitely not running low on available memory.  Processes will sometimes reserve areas of swap even though they aren't actually  swapping which is OK and won't slow down the system since there is no active paging/swapping happening.  What do sar -W and (to a lesser extent) sar -B say about actual active paging/swapping activity?

 

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Re: R80.20 (mlm) log servers swapping

Seems like we have a small, but steady, amount of swapin/outs during load, at night with no load SAR does not register anything.
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Re: R80.20 (mlm) log servers swapping

Doesn't sound too concerning to me, might be interesting to run iotop since you are on the new kernel to see what processes are paging.  If it is just SOLR and LogCore/RFL that is constant log indexing and is expected.

 

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Re: R80.20 (mlm) log servers swapping

Well, on the other system we are now at 2 GB swap in a week. In about 3 weeks we will have a full swap if this continues. Also writing to swap is not desirable on SSD drives, that is why we over provision memory.
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