> Why not implement *true* CLUSTER?
> With cluster, all heap tuples will be in cluster index.
It would be nice. It's pity that pg AMs are not general.
There is no simple way to use btree instead of heap. But
it would help.
But using values from index is good idea too because you
can have table with many columns and aggregate query which
needs only two columns.
The it will be MUCH faster to create secondary index which
is much smaller than heap and use values from it.
Vadim where can I found some code from upcoming WAL ?
I'm thinking about implementing special ranked b-tree
which will store precomputed aggregate values (like
cnt,min,max,sum) in btree node keys. It can be then
used for extremely fast evaluation of aggregates. But
in case of MVCC it is more complicated and I'd like
to see how it would be affected by WAL.
devik