On a production 3 nodes mongodb replicaset we're observing that the db is using only 60% of the ram, then it uses the swap memory. This causes severe slowness at application level.

Parameter "cacheSize" is not set: from the docs we read that by default mongo will use 50% of the avalaible ram minus 1Gb.

OS swappiness parameter is set to 1.

We see that is suggested to avoid increasing WT internal cache size above its default value.

Would it be ok to increase it anyway, in this case?
Otherwise, increasing server ram could be a solution?

Thank you.