On Wed, Aug 3, 2016 at 4:20 AM, Simon Riggs <simon@2ndquadrant.com> wrote:
> == IndexScan ==
>
> Note that the executor code for IndexScan appears identical between
> the two optimizations. The difference between duplicate and range LITE
> tuples is needed only at INSERT time (or UPDATE indexed column to a
> new value).
>
> When we do an IndexScan if we see a LITE tuple we do a scan of the
> linepointer ranges covered by this index tuple (which might eventually
> go to a full block scan). For example with bit1 set we would scan 16
> linepointers (on an 8192 byte block) and with 2 bits set we would scan
> 32 linepointers etc.., not necessarily consecutive ranges. So the
> IndexScan can return potentially many heap rows per index entry, which
> need to be re-checked and may also need to be sorted prior to
> returning them. If no rows are returned we can kill the index pointer,
> just as we do now for btrees, so they will be removed eventually from
> the index without the need for VACUUM. An BitmapIndexScan that sees a
> lossy pointer can also use the lossy TID concept, so we can have
> partially lossy bitmaps.
Wouldn't this risk scanning rows more than once unless it's part of a
bitmap scan?
