On 22.03.2018 23:37, Alvaro Herrera wrote:
> The rd_projidx (list of each nth element in the index list that is a
> projection index) thing looks odd. Wouldn't it make more sense to have
> a list of index OIDs that are projection indexes?
>
rd_projidx is not a list, it is Bitmapset. It is just one of many bitmap
sets in RelationData:
Bitmapset *rd_indexattr; /* identifies columns used in indexes */
Bitmapset *rd_keyattr; /* cols that can be ref'd by foreign
keys */
Bitmapset *rd_pkattr; /* cols included in primary key */
Bitmapset *rd_idattr; /* included in replica identity index */
Yes, it is possible to construct Oid list of projectional indexes
instead of having bitmap which marks some indexes in projectional, but I
am not sure that
it will be more efficient both from CPU and memory footprint point of
view (in most indexes bitmap will consists of just one integer). In any
case, I do not think that it can have some measurable impact on
performance or memory size:
number of indexes and especially projectional indexes will very rarely
exceed 10.
--
Konstantin Knizhnik
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company