After mongodb was started, the find () query was also executed, but the above figure shows mapped as 0. Is mongodb memory mapped at this time? How does mongodb map memory? Can you describe the steps and procedures of memory mapping in detail?
Reference documentserverStatus, with a detailed description of each output item.
mappedAndmappedWithJournalValid for MMAPv1 engine onlyOnly for the MMAPv1 storage engine.
After 3.2, the default storage engine is WiredTiger, so these two values are always 0.
As for the mapping method, MMAPv1 uses the memory mapping of Linux operating system, which cannot be explained here due to space limitation, but there are already a lot of related materials on the internet.