In-Memory Bitmap Index in Postgres

I have written twice already that bitmap indexes are not implemented in Postgres. But somebody may as why then explain writes that it used Bitmap Index Scan? However, that is not on-disk index I wrote about. One of the most interesting analysis of performance I found is at Depesz.com, which is a blog of a Polish database ...

B-tree or Bitmap

Recently I read a lot about databases, mostly theory but also from the design point of view. I have to admit that until recently I had no idea what a B-tree is. I mean beside that it is a kind of a data structure, but how it is build and why on average there is ...