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#mongodb logs for Friday the 26th of March, 2021
[16:13:41] <ws2k3> i have a mongodb running but it uses Alot of ram currently around 8 gb so im trying to limit this so i found this https://stackoverflow.com/questions/6861184/is-there-any-option-to-limit-mongodb-memory-usage but this does not seem to work anyone else got some advice on how to reduce the RAM?
[18:42:06] <d4rkp1r4t3> ws2k3, if you simply reduce the wiredTiger cacheSizeGB you could be inadvertantly increasing disk usage because of having to page more of your workload. if it's using 8gb that means you are running on a server with 16gb total?
[18:42:45] <d4rkp1r4t3> if you really can reduce the cacheSizeGB without impacting your disks, maybe you can just reduce the total memory available for that server
[18:46:53] <d4rkp1r4t3> check out this guys answer here. it explains well how the rest of your memory is being used outside the wt cache. https://dba.stackexchange.com/a/176047
[18:55:04] <ws2k3> d4rkp1r4t3: currently mongod is using 88% of all the ram on my system. so there is nothing i can do about that? cause while reading the documentation i see that if ur system has more then 1GB ram mongod will determine this settings itself. (60% of total)
[19:05:39] <d4rkp1r4t3> yes that is default for the wt cache you are reading about. mongod still has to manage (as the linked answer has eluded us to) it's filesystem cache, 1mb for each connection, in-memory sorts for queries without indexes, and some aggregations.
[19:12:36] <d4rkp1r4t3> if your applications most frequently accessed data (working set) is greater than the amount of memory in the wt cache (uncompressed data), then mongod will yield more to the fs cache (compressed data) and thus could have impact on your disk and cpu.
[19:14:15] <d4rkp1r4t3> ideally your working set fits into the wt cache. by lowering the wt cache you have increased mongod's usage for other things like the fs cache, more connections, more room for in-memory sorts, more room for aggregations.