ve.  Instead,
   we use a pin on an index page as a proxy to indicate that the reader
   might still be <SPAN
CLASS="QUOTE"
>"in flight"</SPAN
> from the index entry to the matching
   heap entry.  Making <CODE
CLASS="FUNCTION"
>ambulkdelete</CODE
> block on such a pin ensures
   that <TT
CLASS="COMMAND"
>VACUUM</TT
> cannot delete the heap entry before the reader
   is done with it.  This solution costs little in run time, and adds blocking
   overhead only in the rare cases where there actually is a confl