Re: sp-gist porting to postgreSQL - Mailing list pgsql-hackers

I believe that it is still possible to have several index access methods for
the same type and the same operations. But this requires that each index
access method has its own tuple in the pg_am relation and therefore
postgresql recognizes it by itself. But this is not the case with GiST based
indices. They are all recognized by postgresql as same index access method,
and from here comes the limitation.

Also, I think GiST and SP-GiST are better viewed as index classes not as
indices by themselves. So may be it is more logical to say:
CREATE INDEX index_name ON table_name USING spgist_trie(field)
Where spgist_trie is an spgist based index instance. 

Than to say:
CREATE INDEX index_name ON table_name USING spgist(field)
And depend on the operator classes to define the required support methods
for the trie function.


I am not sure I have a complete vision, but this is what I see. I would
appreciate your opinions regarding to this design issue.

Thanks
Ramy




-----Original Message-----
From: Oleg Bartunov [mailto:oleg@sai.msu.su] 
Sent: Wednesday, November 10, 2004 5:21 AM
To: Ramy M. Hassan
Cc: 'Pgsql Hackers'; 'Teodor Sigaev'; 'Walid G. Aref'
Subject: RE: sp-gist porting to postgreSQL

On Wed, 10 Nov 2004, Ramy M. Hassan wrote:

> Oleg,
>
> Thanks for your prompt reply.
> Actually, I am able to create a new access method for testing and add an
> operator class for the type "integer" using the new access method. Then
> created a table with two integer fields, one indexed using the new access
> method and the other using a btree index, and everything is ok so far.
Even
> using EXPLAIN statement for queries show that the indexes are used
correctly
> as they should.
> I am using postgresql version 8.0.0beta3 from CVS.

I was wrong, Ramy. You could have several indices for the same type as soon
as they support different operations. I don't know if it's possible
to have them for the same operation but for different conditions.

>
> Thanks
> Ramy
>
>
>
> -----Original Message-----
> From: Oleg Bartunov [mailto:oleg@sai.msu.su]
> Sent: Wednesday, November 10, 2004 12:35 AM
> To: Ramy M. Hassan; Pgsql Hackers
> Cc: Teodor Sigaev; Walid G. Aref
> Subject: Re: sp-gist porting to postgreSQL
>
> Ramy,
>
> glad to hear from you !
> AFAIK, posgresql doesnt' supports several indices for the same type.
> I think this is a problem of optimizer. Probably other hackers know
> better. I forward your message to -hackers mailing list which is a
> relevant place for GiST discussion.
>
>     regards,
>         Oleg
>
>
> On Tue, 9 Nov 2004, Ramy M. Hassan wrote:
>
>> Dear Oleg and Teodor,
>> Thanks for offering help.
>> I have a design question for now.
>> Currently in the postgresql GiST implementation, I noticed that the way
to
>
>> have a GiST based index is to define an operator class for a certain type
>> using GiST index. There is no new index type defined from the point of
> view
>> of postgresql ( nothing is added to pg_am ). This means that for a
certain
>
>> type there could only be one GiST based index. I mean that there is no
way
> in
>> the same server to use gist to implement an xtree index and a ytree  for
> the
>> same  type even if they index different fields in different relations. is
>> that correct ?
>> What about doing it the other way ( I am talking about SP-GiST now ) , by
>> providing the extension writer with an API to use it to instantiate a
>> standalone SP-GiST based index ( for example trie index ) that has a
> record
>> in the pg_am relation. In my point of view this would give more
> flexibility,
>> and also would not require the extension writer to learn the postgresql
> API (
>> maybe oneday SP-GiST will be ported to another database engine )  he will
>> just need to learn the SP-GiST API which will propably be less amount of
>> study  (and this is what GiST and SP-GiST is all about if I correctly
>> understand ).
>> Please let me know your opinions regarding to this.
>>
>> Thanks
>>
>> Ramy
>>
>
>     Regards,
>         Oleg
> _____________________________________________________________
> Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
> Sternberg Astronomical Institute, Moscow University (Russia)
> Internet: oleg@sai.msu.su, http://www.sai.msu.su/~megera/
> phone: +007(095)939-16-83, +007(095)939-23-83
>
    Regards,        Oleg
_____________________________________________________________
Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
Sternberg Astronomical Institute, Moscow University (Russia)
Internet: oleg@sai.msu.su, http://www.sai.msu.su/~megera/
phone: +007(095)939-16-83, +007(095)939-23-83