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Currently, to set the WiredTiger cache size in MBs, rather than GBs, we're forced to do so via a commandline option (which isn't listed in the docs, or via mongod --help). This makes the assumption that nearly everyone using MongoDB has or needs large server requirements to work with, and ignores users who run services/sites/application from smaller setups (in particular, VMs). Also, as mentioned, the command arg to limit the size to MBs isn't listed, and I found it on the mongodb-user google group page: https://groups.google.com/forum/#!msg/mongodb-user/V2Q4LZAe2m0/pqNSu4psDQAJ Specifically: --wiredTigerEngineConfigString="cache_size=xxxM"

Top User Comments

ramon.fernandez commented on Sun, 10 Jul 2016 22:22:17 +0000: antonio-malcolm, please see this comment explaining how to set the cache size in MBs in the config file. Regards, Ramón. dan@10gen.com commented on Sun, 10 Jul 2016 14:33:03 +0000: This is fixed in SERVER-23624 and will be available in 3.4 antonio-malcolm commented on Sun, 10 Jul 2016 00:31:37 +0000: Well, I just answered my own question: Error parsing option "storage.wiredTiger.engineConfig.cacheSizeGB" as int: Bad digit "." while parsing 0.25 So, your documentation is off- it needs an int, not a number. In any case, a setting lower than 1GB should be available, without resorting to an undocumented command line arg. antonio-malcolm commented on Sat, 9 Jul 2016 23:45:40 +0000: OK, I just noticed the distinction, in the MongoDB docs, between , as the value type, and , with used to set the cache size. Does this mean decimal values can be used, for the cache and in-memory sizes? That would satisfy this ticket. Also, it appears, in one of your rmore recent code changes, the use of Double was employed.... but as that was a very small subsection of your overall code base, I don't want to jump to conclusions.

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