On Wed, Aug 3, 2016 at 4:20 AM, Simon Riggs <si...@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? -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
