[fdo-internals] RFC 26 - New Extended Select commandandScrollable Reader - for review

[Orest Halustchak]

Hi Jason,

Yes, I think this might work better in the standard select with regular forward-only reader.

Orest.

From: fdo-internals-bounces at lists.osgeo.org [mailto:fdo-internals-bounces at lists.osgeo.org] On Behalf Of Jason Birch
Sent: Monday, October 20, 2008 4:06 PM
To: FDO Internals Mail List
Subject: RE: [fdo-internals] RFC 26 - New Extended Select commandandScrollable Reader - for review

I was thinking something that limited the total records that were returned; everything outside of the limit window (start record, num rows) would not be accessible via the api at all.  Additional results would require a second select.  This might be a better fit for the standard select than the scrollable reader?

To clarify, in SQL I would do something like this for the first page of results:

SELECT id, name
FROM tablename
LIMIT 0,20

And this for the second page:

SELECT id, name
FROM tablename
LIMIT 20,20

Etc, etc,

Because HTTP is stateless, there is no reason to make rows outside of the selected set available, unless there is some kind of feature cache at the FDO level that would make subsequent selects more efficient.

Jason

From: fdo-internals-bounces at lists.osgeo.org [mailto:fdo-internals-bounces at lists.osgeo.org] On Behalf Of Orest Halustchak
Sent: Monday, October 20, 2008 12:49
To: FDO Internals Mail List
Subject: RE: [fdo-internals] RFC 26 - New Extended Select commandandScrollable Reader - for review

Hi Jason,

So, this limit would be something that would return an end of fetch after reading 'limit' number of records? But, then you can reset it I guess when you want to get the next page (maybe just by calling ReadAtIndex() again). An issue with the scrollable reader is that you can read forwards or backwards, and jump to a new record index at any time. So, I think adding a limit would complicate this mechanism - knowing when to reset it or what it means after jumping to a new record.

Thanks,
Orest.


From: fdo-internals-bounces at lists.osgeo.org [mailto:fdo-internals-bounces at lists.osgeo.org] On Behalf Of Jason Birch
Sent: Monday, October 20, 2008 3:03 PM
To: FDO Internals Mail List
Subject: RE: [fdo-internals] RFC 26 - New Extended Select command andScrollable Reader - for review

I don't have any direct experience with this because MapGuide doesn't currently doesn't allow access to these commands.  I certainly see value in making these part of the common feature set though.  Maybe I'll eventually be able to do sorting on SDF results via MapGuide :)

One thing that occurred to me when reading this RFC was that I'd like to see a mechanism to "page" through results; similar to the LIMIT clause in MySQL.  When displaying result sets in a web environment, you often want to give the user a small set of the data, and then page through the results N records at a time.  I can currently brute-force this, but it would be more efficient to handle this on the FDO side, especially for providers where the underlying storage format has optimized methods of dealing with it.  The current enhancements would make this more efficient to brute-force, but I wonder if adding parameters to the initial selection (start record, number of results) would make this even more efficient.

Jason

From: fdo-internals-bounces at lists.osgeo.org [mailto:fdo-internals-bounces at lists.osgeo.org] On Behalf Of Orest Halustchak
Sent: Monday, October 20, 2008 11:24
To: FDO Internals Mail List
Subject: RE: [fdo-internals] RFC 26 - New Extended Select command andScrollable Reader - for review

Hi,

I wonder if anyone has any comments on this. If nobody has any objections to it, I'd like to bring it to a vote soon.

Thanks,
Orest.

From: fdo-internals-bounces at lists.osgeo.org [mailto:fdo-internals-bounces at lists.osgeo.org] On Behalf Of Orest Halustchak
Sent: Friday, October 17, 2008 12:37 PM
To: FDO Internals Mail List
Subject: [fdo-internals] RFC 26 - New Extended Select command and Scrollable Reader - for review

Hi,

I'd like to bring your attention to RFC 26 ( http://trac.osgeo.org/fdo/wiki/FDORfc26 ) which proposes to add a new Extended Select command with uses a Scrollable feature reader. Basically, this takes what currently are custom commands in the SDF, SHP, and recently SQLite providers and makes them generic FDO commands. This will remove special case handling for applications that currently use these and open the door for generic use by any application.

Please review and provide your feedback.

Thanks,
Orest.

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