metadata.json的位置存在metastore中，metadata.json存当前快照
    ${number}-${uuid}.metadata.json -> metadata file
    00176-fd8ba4ca-2e84-415b-9260-8c2ee5d59444.metadata.json

    snap-*.avro -> manifest list
    snap-7112904555092462618-1-9ab41d1a-d41d-45a1-8be5-e8b49a49f6e4.avro

    -m.avro -> manifest file
    c85f3931-d913-4328-adae-e09e33529a11-m0.avro