Re: index structure for 114-dimension vector

Andrew Lazarus wrote:
> Because I know the 25 closest are going to be fairly close in each
> coordinate, I did try a multicolumn index on the last 6 columns and
> used a +/- 0.1 or 0.2 tolerance on each. (The 25 best are very probably inside
> that hypercube on the distribution of data in question.)
>
> This hypercube tended to have 10-20K records, and took at least 4
> seconds to retrieve. I was a little surprised by how long that took.
> So I'm wondering if my data representation is off the wall.
>
> I should mention I also tried a cube index using gist on all 114
> elements, but CREATE INDEX hadn't finished in 36 hours, when I killed
> it, and I wasn't in retrospect sure an index that took something like
> 6GB by itself would be helpful on a 2GB of RAM box.
>
> MK> I don't think that will work for the vector norm i.e:
>
> MK> |x - y| = sqrt(sum over j ((x[j] - y[j])^2))
>
>

Sorry, in that case it probably *is* worth trying out 6 single column
indexes and seeing if they get bitmap and'ed together...

Mark