Duplicate:

< * Maintain a map of recently-expired rows
<
<   This allows vacuum to target specific pages for possible free space
<   without requiring a sequential scan.
<
Update entry:

>   One complexity is that index entries still have to be vacuumed, and
>   doing this without an index scan (by using the heap values to find the
>   index entry) might be slow and unreliable, especially for user-defined
>   index functions.