Userdata column in CI session.

What exactly the Value in userdata column of CI session table interprets. This data is in serialize form.Can anybody explain this field value.

Its all of the custom session data that you set, which gets serialized and stored in a single field in the db. In CI2 it's a slightly custom format. In CI3, it's the native $_SESSION format (like if you were to open a session file).

The data present in session_userdata is in array form.