30e2dc02f0
Summary: A recent change introduced readahead inside VerifyChecksum(). However it is not compatible with mmap mode and generated wrong checksum verification failure. Fix it by not enabling readahead in mmap mode. Pull Request resolved: https://github.com/facebook/rocksdb/pull/5945 Test Plan: Add a unit test that used to fail. Differential Revision: D18021443 fbshipit-source-id: 6f2eb600f81b26edb02222563a4006869d576bff