Re: Need help for our thesis.

Hello Mika

Currently you can use dblink which queries a remote database and returns
the data as a table. This works nicely for PostgreSQL. There is also a
JDBC version in progress.
We have writte an Oracle version of dblink.

SELECT * FROM dblink('connectstr', 'SELECT ...') AS some_type;

This works nicely.
Still, this is not a full implementation of distributed queries - this
would be a huge project. There has already been some discussion about
that on the hackers list.

Regards,

Hans

Richard Schilling wrote:
> As luck would have I've put some thought into this problem before as
> well. Having reviewed the code quite a bit, and played around with the
> backend, my intuition tells me that the following would work.
>
> Write a custom "cluster-aware" postmaster so it distributes queries to
> various machines. Of course each machine would have to be running a
> normal postmaster to receive the queries. And, the cluster-aware
> postmaster would need to be informed of which machines to submit queries
> to (e.g. listed in a configuration file). Queries could be processed in
> the following ways:
>
> * database management queries (e.g. create database, create table,
> alter table, etc. . . ) would be distributed to every machine
> * select queries would be distributed to every machine. The
> cluster-aware postmaster would merge the results before delivering them
> to the client.
> * an insert query would go to one machine only, and the
> cluster-aware postmaster could switch between the designated machines
> after each insert. For example, given two machines, the first insert
> would go to machine A, the second to machine B, etc . . .
>
> Don't know if that's been tried, but that's where I would start.
> Postgres' modular design of a postmaster and a backend would make this
> relatively easy to do, because the only thing you might end up writing
> is the one cluster-aware postmaster. If you end up doing this let me
> know and if I have time I'll help out with the design/coding.
>
> Richard Schilling
> Lake Stevens, WA USA
>
>
>
> On 2003.07.04 18:56 MIka Santos wrote:
>
>> Gud day! We are currently having our thesis for our undergarduate
>> course and this involoves the code of PostgreSQL. Basically, our
>> thesis needs a modification of the existing code of the said database.
>> As of now, our University has an existing online registration system
>> which uses Postgre as their back end. But the problem is the existing
>> one is not a distributed system. Our thesis adviser would like us to
>> deal with the load balancing of the said online registration. He
>> wanted a multidatabase querying. For example, we knew that the
>> following statements are posible,
>> select *
>> from t1, t2., t3;
>> provided that t1 and t2, t3 are tables from a single database.
>> Our thesis is to make the following satatement legal
>> select *
>> from d1, d2, d3;
>> provided that d1 and d2, d3 are separate databases.
>> We are currently having our research about this problem and as
>> beginners, we surely need help from experts like you. Any form of
>> comments and suggestions will surely be appreciated by the group.
>> Thank you very much and hope to here from you.

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