On Mar 27, 2015 11:08 AM, Dima Ivanovskiy dima...@mail.ru wrote:
Hello, I am Dmitrii, student of Moscow Institute of Physics and Technology
Abstract:
I chose project Indexing prolonged geometrical objects (i.e. boxes,
circles, polygons, not points) with SP-GiST by mapping to 4d-space.
According to the presentation
https://www.pgcon.org/2011/schedule/attachments/197_pgcon-2011.pdf
SP-GIST 3 times faster than GiST in some cases. But GIST supports
geometrical data types:
box, circle, polygon with operators:| | @ @ @ | |
~ ~=
Popular spatial extension PostGIS doesn't include SP-GIST, but has a lot of
geometrical features.
Project details:
After meeting with Alexander Korotkov, I wrote some plan.
Using of K-D-tree and Quadtree in building index for geometrical data types
can increase speed of search in some cases.
The main idea is representing 2-D geometrical objects in their bounding box.
Set of 2-D boxes is 4-D space.
New _ops will work with points from 4-D space, for example kd_box_ops,
quad_circle_ops and will support all geometrical operators.
After conversion object to their bounding box algo has set of tuples (x1,
y1, x2, y2).
Our goal is separate this space the most equally. If we talk about K-D-tree,
on first step K-D-tree algorithm will split space in 2 parts by the first
coordinate, in next step by the second coordinate etc., after 4-th
coordinate we repeat this procedure.
At the end we have index at geometrical objects and use traversal tree for
every search operator.
Postgresql has already has realization ideas of MBR in gist/gistproc.c. So I
will transfer this realization to other type of tree.
Of cource, I assume that SP-GIST can be not the best decision of this
problem. So after testing this clear methods, I will try to find more
effective way. Maybe with using combination of different spatial tree
structures.
Project Schedule:
until May 25
Read documentation and source code, clarify details of implementation.
1st month
Implement new '_ops' with all geometrical operators for box, circle, polygon
2nd month
Research new methods for increase speed of geometrical query
3rd month
Final refactoring, testing and submitting a patch.
Links:
http://www.sai.msu.su/~megera/postgres/talks/gist_tutorial.html - about GIST
https://toster.ru/q/27135#answer_110197 - people need SP-GIST for cubes
http://www.slideshare.net/profyclub_ru/o-lt - presentation about indexes
http://pgconf.ru/static/presentations/2015/korotkov_spatial.pdf - working
with geo objects
Nice proposal.
Dynamic Kdtrees can perform badly as the splitting median can get way off as
updates are coming. What are your thoughts about that?
Also what's up with the 4d space? I don't quite get it. These types are 2 or 3
dimensions.
I read spgist README one more time . I didn't find the mechanism for
maintaining good balance after updates.
I think we can use Bkd-Tree,
https://www.cs.duke.edu/~pankaj/publications/papers/bkd-sstd.pdf . But It can
be not the best solving.
I include Research time in 2nd month of timeline.
About 4d space. All these types are 2 dimensional.
Just as i n R-tree object is approximated by MBR. MBR for 2d-objects can be
mapped to 4d-point. More general, nd-object MBR can be mapped into 2nd-point.
