On Thu, Aug 4, 2016 at 1:58 PM, Simon Riggs <si...@2ndquadrant.com> wrote: > On 3 August 2016 at 20:37, Claudio Freire <klaussfre...@gmail.com> wrote: >> 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? > > It's always the job of the index insert logic to ensure a valid index exists. > > I'm not sure what you see that changes that here. Say more?
I just explained it further in the WARM thread, which is actually the idea I was arriving to. -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
