Re: Hash index todo list item

Ühel kenal päeval, E, 2007-09-03 kell 19:55, kirjutas Tom Lane:
> Gregory Stark <stark(at)enterprisedb(dot)com> writes:
> > "Kenneth Marshall" <ktm(at)rice(dot)edu> writes:
> >> - What about multi-column indexes? The current implementation
> >> only supports 1 column.
>
> > That seems kind of weird. It seems obvious that you mix the three hashes
> > together which reduces it to the solved problem.
>
> No, because part of the deal is that you can do lookups using only the
> leading index columns. At least, all the existing multicolumn index
> types can do that.

One approahc is not to mix hashes, but to partition the hash, so that
each column gets its N bits in the hash.

If you do it smartly you can use any column for index lookups, not just
the leading one.

> regards, tom lane
>
> ---------------------------(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