From: | Indra Heckenbach <indra(at)macnica(dot)com> |
---|---|
To: | Oliver Jowett <oliver(at)opencloud(dot)com> |
Cc: | pgsql-jdbc(at)postgresql(dot)org |
Subject: | Re: absolute positioning |
Date: | 2004-03-24 07:29:36 |
Message-ID: | 406138E0.8090501@macnica.com |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-jdbc |
Hi Oliver,
Thanks for pointing me to this discussion. From what I can tell, work must have been done on the postgres backend to improve support for cursors. I have been using cursors with fairly complex queries (joins and nested subqueries and order bys) without any problems.
I went ahead and patched the JDBC jar from the CVS head on gborg. This patch should enable scrollable cursor support, and provide absolute() w/o loading all results into the JDBC buffer. Unfortunately, the patch involves changing some core aspects of the driver. I have not reviewed the existing code thoroughly, so I could have introduced problems. I have also not tested extensively. However, the patch works for me, and I could use the patched driver with existing applications. Is there a test suite for the driver? At this point I hope to get some feedback.
Here is a summary of the patch:
AbstractJdbc1ResultSet
- added "buffer_row" and "cursor_row" to track cursor and buffer position. remove "current_row", and use these instead.
- use a new variable "needsRefresh" to control reload state explicitly
- convert next() method to load on demand instead of pre-load. the former method does not work with cursor positioning, or would require a hack to load data twice, and support multiple modes of loading.
Abstract1Jdbc1Statement
- to prevent pre-load, I made the while loop over reallyResultSet() occur only if cursors are disabled. I don't think this is needed in this context for cursors, but I'm not certain.
- added DECLARE SCROLL CURSOR to handle scrollable case.
AbstractJdbc2ResultSet
- use a new variable "internalIndex" in AbstractJdbc2ResultSet to track absolute position, to avoid overlapping repositioning.
- implement absolute() as FETCH ABSOLUTE. relative() uses this code, so it should be supported as well.
thanks,
Indra
Oliver Jowett wrote:
Indra Heckenbach wrote:
Thanks for the info. So the implementation is functional, but does so by preventing cursors. Unfortunately, I am dealing with a large result set, so I need to use cursors. I started modifying the jdbc driver. Any other suggestions?
There was a discussion about implementing this a couple of months ago that might be useful to you, starting at: http://archives.postgresql.org/pgsql-jdbc/2004-01/msg00288.php
-O
Attachment | Content-Type | Size |
---|---|---|
unknown_filename | text/html | 3.3 KB |
cursor_patch.diff.gz | application/x-gzip | 2.1 KB |
From | Date | Subject | |
---|---|---|---|
Next Message | Oliver Jowett | 2004-03-24 09:16:46 | Re: absolute positioning |
Previous Message | dinakar | 2004-03-24 04:57:35 | Re: Postmaster not dropping connections on tomcat restart. |