# Consistent View
+ Snapshot
  + Essentially is a sequence number
    + Increased monotonically after writing to each key
    + Every key has a sequence number
      + Used to support versioning for `MVCC`
  + Monitored by `flush` and `compaction` operations to preserve visible keys
+ `SuperVersion`
  + The current version of `LSM-tree + MemTable`
  + Could prevent stale files from being deleted

| `uKey` | `Sequence Number` (7 bytes) | `Type` (1 byte) |
| :----- | :-------------------------- | :-------------- |
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