Lucene mmap usage config

I noticed “Make Lucene mmap usage configurable (#4283)” in the release notes but didn’t see anything in the documentation about what the configuration property was.

Hi Zach,

It’s a “hidden” feature that is undocumented, for now. Basically, if you set index.lucene.mmap=false in your, both search and spatial indices will not use memory mapped files.


Just curious but why would someone want to use that? I’m guessing it’s using RAMDirectory and heap memory.

No, RAMDirectory is never used. If that option is turned off the NIOFSDirectory will be used. Someone might want to do that if the system has issues with memory mapping (sometimes containers might have that problem). We think most of the time that option should not be necessary but it is there just in case.


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