Re: Re: 7.2 items

I think it's possible to implement bitmap indexes with a little
effort using GiST. at least I know one implementation
http://www.it.iitb.ernet.in/~rvijay/dbms/proj/
if you have interests you could implement bitmap indexes yourself
unfortunately, we're very busy

Oleg
On Thu, 7 Jun 2001, mlw wrote:

> Bruce Momjian wrote:
>
> > > Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> > >
> > > > Here is a small list of big TODO items. I was wondering which ones
> > > > people were thinking about for 7.2?
> > >
> > > A friend of mine wants to use PostgreSQL instead of Oracle for a large
> > > application, but has run into a snag when speed comparisons looked
> > > good until the Oracle folks added a couple of BITMAP indexes. I can't
> > > recall seeing any discussion about that here -- are there any plans?
> >
> > It is not on our list and I am not sure what they do.
>
> Do you have access to any Oracle Documentation? There is a good explanation
> of them.
>
> However, I will try to explain.
>
> If you have a table, locations. It has 1,000,000 records.
>
> In oracle you do this:
>
> create bitmap index bitmap_foo on locations (state) ;
>
> For each unique value of 'state' oracle will create a bitmap with 1,000,000
> bits in it. With a one representing a match and a zero representing no
> match. Record '0' in the table is represented by bit '0' in the bitmap,
> record '1' is represented by bit '1', record two by bit '2' and so on.
>
> In a table where comparatively few different values are to be indexed in a
> large table, a bitmap index can be quite small and not suffer the N * log(N)
> disk I/O most tree based indexes suffer. If the bitmap is fairly sparse or
> dense (or have periods of denseness and sparseness), it can be compressed
> very efficiently as well.
>
> When the statement:
>
> select * from locations where state = 'MA';
>
> Is executed, the bitmap is read into memory in very few disk operations.
> (Perhaps even as few as one or two). It is a simple operation of rifling
> through the bitmap for '1's that indicate the record has the property,
> 'state' = 'MA';
>
>
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>
> http://www.postgresql.org/search.mpl
>

Regards,
Oleg
_____________________________________________________________
Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
Sternberg Astronomical Institute, Moscow University (Russia)
Internet: oleg(at)sai(dot)msu(dot)su, http://www.sai.msu.su/~megera/
phone: +007(095)939-16-83, +007(095)939-23-83