Untitled

+--------+--------+---------------------------+
| PK     | SK     | (Attributes)              |
+-----------------+---------------------------+
| UserId | UserId | username, profile, etc... |  <-- user item
| UserId | PostId | body, timestamp, etc...   |  <-- post item
+--------+--------+---------------------------+

{
  "userId": <UserId>",
  "body": <Body>,
  etc...
}