Re: JDBC 2 ResultSet and cursors - Mailing list pgsql-jdbc

To use a cursor behind the scenes would require the jdbc driver to have its own begin/end
block.  Because the connection is shared, there is nothing that prevents someone else from
trying to execute a begin/end/commit/rollback statement that would screw up the driver.
So it would need a seperate connection for each scrollable resultset.

Kovács Péter wrote:

> I am afraid I do not understand your explanation. What do you mean by
> "begin/end block"? I am thinking in terms of simple SQL statements like:
>
> begin;
> declare myc cursor for select * from mm_history;
> fetch forward 2 in myc;
> close myc;
> rollback; (or if you did some update in the same transaction: commit;)
>
>
>
>>-----Original Message-----
>>From: Joseph Shraibman [mailto:jks@selectacast.net]
>>Sent: Tuesday, October 16, 2001 11:54 PM
>>To: Kovács Péter
>>Cc: pgsql-jdbc@postgresql.org
>>Subject: Re: JDBC 2 ResultSet and cursors
>>
>>
>>Because the driver would have to dedicate a connection to the
>>backend to the resultset to
>>make sure nobody else tries to begin/end a block while it is
>>trying to use a cursor.
>>(that's the simple explanation)  Since a connection to the
>>backend currently requires a
>>fork, it would be a real resource hog.
>>
>>Kovács Péter wrote:
>>
>>
>>>Hi,
>>>
>>>I have a question for which I can think of an answer, but still I am
>>>uncertain about it.
>>>
>>>Why the scrollable result sets are not implemented in the
>>>
>>current jdbc
>>
>>>driver? Is it technically impossible or just no one needed
>>>
>>this feature yet?
>>
>>>The answer is probably that due to the lack of backend
>>>
>>support for updatable
>>
>>>cursors the scrollable result set would not be fully
>>>
>>functional. (On the
>>
>>>face of it, I think that it should be possible to build support for
>>>read-only scrollable result set into the jdbc driver.) But
>>>
>>would a halfway
>>
>>>solution not be better than nothing? You need to resort to
>>>
>>workarounds
>>
>>>anyway, if you want to use cursor based data processing
>>>
>>with PostgreSQL.
>>
>>>IMHO, a read-only scrollable result set would definitly be
>>>
>>an important step
>>
>>>toward code portability.
>>>
>>>Any comments?
>>>
>>>Does anyone have info on whether there are plans to
>>>
>>implement support for
>>
>>>updatable cursors in the backend? If there are, what are they?
>>>
>>>Thank you
>>>
>>>Peter
>>>
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>>>
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>>
>>--
>>Joseph Shraibman
>>jks@selectacast.net
>>Increase signal to noise ratio.  http://www.targabot.com
>>
>>


--
Joseph Shraibman
jks@selectacast.net
Increase signal to noise ratio.  http://www.targabot.com