Although storing millions of files is feasible, billions is beyond the capability of current hardware.
AMD/Intel Server processors support upto 1.5 TB of memory. In such case, it is possible to hold 4-5 billion files in memory. (3.3 million files per GB => 3.3*1500 = 4950 million files) This point needs revisit. In worst scenario, it must be possible to keep at least a billion files...
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