1.`/mem_tracker?type=global` to view the memory statistics of each type, `global`life cycle is the same as the process, e.g. each Cache, StorageEngine, each Manager.
2.`/mem_tracker` counts virtual memory, which is equal to `Actual memory used` in `/memz`
3.`process` is equal to the sum of all types of memory, `/mem_tracker` can be logically divided into 4 layers: 1)`process` 2)`type` 3)`query/load/compation task etc.` 4)`exec node etc.`