> > These numbers don't make much sense to me. It seems like 5% is about as slow
> > as reading the whole file which is even worse than I expected. I thought I
> > was
> > being a bit pessimistic to think reading 5% would be as slow as reading 20%
> > of
> > the table.
I have a theory. My test program, like Postgres, is reading in 8k chunks.
Perhaps that's fooling Linux into thinking it's a sequential read and reading
in 32k chunks internally. That would effectively make a 25% scan a full table
scan. And a 5% scan would be a 20% scan which is about where I would have
expected the breakeven point to be.
--
greg
---------------------------(end of broadcast)---------------------------
TIP 9: In versions below 8.0, the planner will ignore your desire to
choose an index scan if your joining column's datatypes do not
match
