Re: GiST index implementation

Hi Gregory,

thank you very much for you answer!

>
> > what is the default implementation for GiST index? B-Tree or R-Tree?
> > That is, if i execute the following SQL command:
> >
> > CREATE index ON table USING Gist (column)
> >
> > what is the type of the index that is actually built?
>
> uhm, GIST. GIST is a particular type of index just like btree.

according to the documentation (ch 11.2) "GiST indexes are not a single kind
of index, but rather an infrastructure within wich many different indexing
strategies can be implemented", and (ch 50.1) "B-Tree, R-Tree and many other
indexing schemes can be implemented in GiST".
Moreover, according to what i found on the web (see
http://www.sai.msu.su/~megera/postgres/gist/ ) some of such implementations
are now included in the core of Postgres.
I supposed there was a way to specify one among the implementation
provided.

What are you actually trying to do? Do you have a particular problem you're
> trying to solve?

I wanted to test the suitability and the efficiency of R-Tree/GiST for
query involving standard PostgreSQL temporal column data.

> How can I specify in SQL one of the two implementations provided (e.g.
> > R-Tree)?
>
> R-Tree indexes don't exist in Postgres any more. GIST indexes are very
> similar
> only more general. They handle 2D geometric data types like RTree did
> previously as well as n-dimensional data types and other more exotic
> things
> like intarrays and full text search.

Are these functionalities all included by default in the standard GiST
indexing?

There are different "kinds" of GIST indexes which you can specify by
> specifying an operator class with you define the index.

But most data types
> only have a single operator class available to them so that's probably not
> what you need unless you're trying to do something unusual.

An "operator class" defines a set of operators which can be optimized by an
> index organized the same way and usually correspond to a particular
> interpretation of the data type.

Is the specification of the operator class done when I create the index?
Or is the suitable operator class automatically loaded according to the
data type of the column on which I build the index?
And if I would specify a different operator class, how can i do it?
May I provide a different operator class beyond the ones provided?

Thank you very much.

Regards,
-Elena