Hi,

I'm trying to add a -project specific- networking feature to my postgres
build (or database as function). What I want to do is to send a Query
instance (as a String-retrieved through an SPI function) to other
machines and (after they have executed it) to receive result tuples.
It's about a mediator-wrapper project. My first thought was to write 2
SPI functions (one for the server (concurrent) and the other for client)
but I'm not sure if this is going to work. I'm worried about setting up
the server process running on the background while other SPI calls are
made.

Can this be done? Should I consider something else first, before 
writting any code? 
Any suggestions would be appreciated!

Best regards,
Ntinos Katsaros




14 Oct 2004 10:54:12 +0300
"Katsaros Kwn/nos" <ntinos@aueb.gr>
Networking feature for postgresql...
Katsaros Kwn/nos wrote:
> Hi,
> 
> I'm trying to add a -project specific- networking feature to my postgres
> build (or database as function). What I want to do is to send a Query
> instance (as a String-retrieved through an SPI function) to other
> machines and (after they have executed it) to receive result tuples.
> It's about a mediator-wrapper project. My first thought was to write 2
> SPI functions (one for the server (concurrent) and the other for client)
> but I'm not sure if this is going to work. I'm worried about setting up
> the server process running on the background while other SPI calls are
> made.

Have you looked at the dblink code?

-- 
   Richard Huxton
   Archonet Ltd

Thu, 14 Oct 2004 09:15:31 +0100
Richard Huxton <dev@archonet.com>
Re: Networking feature for postgresql...
Well, actually no :) ! Thanks for the hint!

But just from curiosity, would the scenario I described work?
I mean is it possible for an SPI process to run in the background while
other SPI calls are made?

Ntinos Katsaros


On Thu, 2004-10-14 at 11:15, Richard Huxton wrote:
> Katsaros Kwn/nos wrote:
> > Hi,
> > 
> > I'm trying to add a -project specific- networking feature to my postgres
> > build (or database as function). What I want to do is to send a Query
> > instance (as a String-retrieved through an SPI function) to other
> > machines and (after they have executed it) to receive result tuples.
> > It's about a mediator-wrapper project. My first thought was to write 2
> > SPI functions (one for the server (concurrent) and the other for client)
> > but I'm not sure if this is going to work. I'm worried about setting up
> > the server process running on the background while other SPI calls are
> > made.
> 
> Have you looked at the dblink code?


14 Oct 2004 11:36:15 +0300
"Katsaros Kwn/nos" <ntinos@aueb.gr>
Re: Networking feature for postgresql...
Katsaros Kwn/nos wrote:
> Well, actually no :) ! Thanks for the hint!
> 
> But just from curiosity, would the scenario I described work?
> I mean is it possible for an SPI process to run in the background while
> other SPI calls are made?

I don't think so, you're running in a backend process, so you'd need to 
fork the backend itself.

> On Thu, 2004-10-14 at 11:15, Richard Huxton wrote:
> 
>>Katsaros Kwn/nos wrote:
>>
>>>Hi,
>>>
>>>I'm trying to add a -project specific- networking feature to my postgres
>>>build (or database as function). What I want to do is to send a Query
>>>instance (as a String-retrieved through an SPI function) to other
>>>machines and (after they have executed it) to receive result tuples.
>>>It's about a mediator-wrapper project. My first thought was to write 2
>>>SPI functions (one for the server (concurrent) and the other for client)
>>>but I'm not sure if this is going to work. I'm worried about setting up
>>>the server process running on the background while other SPI calls are
>>>made.
>>
>>Have you looked at the dblink code?


-- 
   Richard Huxton
   Archonet Ltd

Thu, 14 Oct 2004 09:57:55 +0100
Richard Huxton <dev@archonet.com>
Re: Networking feature for postgresql...
Hi again,

Having taken a look at the dblink code I have some questions:

Having a user defined function, is it possible -with no serious memory
overheads- to fork it (outside SPI calls code) in order to make
concurrent dblink calls? What I'm thinking of doing is to create a
function which opens an SPI session, creates some objects (Query nodes),
closes it and then forks as many times as the number of required dblink
calls (having available the appropriate Query node, something like
for(all nodes) fork();...).

My guess is that it is possible cause the backend calls for dblink are
done on the other side (when speaking for Select statements
only).However the returned tuples can only be merged (to produce the
final result) in main memory cause storing them first (e.g. temp table)
would  need concurrent SPI calls.Am I right? If so is there any
mechanism that can multiplex this storing procedures?

On the other side, I suppose a server can serve multiple incoming
queries.

Regards,
Ntinos Katsaros


On Thu, 2004-10-14 at 11:57, Richard Huxton wrote:
> Katsaros Kwn/nos wrote:
> > Well, actually no :) ! Thanks for the hint!
> > 
> > But just from curiosity, would the scenario I described work?
> > I mean is it possible for an SPI process to run in the background while
> > other SPI calls are made?
> 
> I don't think so, you're running in a backend process, so you'd need to 
> fork the backend itself.
> 
> > On Thu, 2004-10-14 at 11:15, Richard Huxton wrote:
> > 
> >>Katsaros Kwn/nos wrote:
> >>
> >>>Hi,
> >>>
> >>>I'm trying to add a -project specific- networking feature to my postgres
> >>>build (or database as function). What I want to do is to send a Query
> >>>instance (as a String-retrieved through an SPI function) to other
> >>>machines and (after they have executed it) to receive result tuples.
> >>>It's about a mediator-wrapper project. My first thought was to write 2
> >>>SPI functions (one for the server (concurrent) and the other for client)
> >>>but I'm not sure if this is going to work. I'm worried about setting up
> >>>the server process running on the background while other SPI calls are
> >>>made.
> >>
> >>Have you looked at the dblink code?
> 


16 Oct 2004 13:40:26 +0300
"Katsaros Kwn/nos" <ntinos@aueb.gr>
Re: Networking feature for postgresql...
Katsaros Kwn/nos wrote:
  > Having taken a look at the dblink code I have some questions:
> 

ISTM that you might start with dblink_record() and modify it to suit 
using SPI and asynchronous libpq calls. See:
http://www.postgresql.org/docs/current/static/libpq-async.html

Joe

Sat, 16 Oct 2004 09:48:47 -0700
Joe Conway <mail@joeconway.com>
Re: [HACKERS] Networking feature for postgresql...