[fdo-internals] Counting rows in managed IFeatureReader

Orest Halustchak orest.halustchak at autodesk.com
Wed Apr 23 12:30:50 EDT 2008

Even with transactional support, you don't have a guarantee that two selects will return the same results unless the server supports a snapshot or serializable type of transaction isolation level, which is not usually default. Typical isolation levels are read-committed. But, this would be the same case regardless of whether you did a select aggregates and then a select versus running a select twice.


-----Original Message-----
From: fdo-internals-bounces at lists.osgeo.org [mailto:fdo-internals-bounces at lists.osgeo.org] On Behalf Of Jason Birch
Sent: Wednesday, April 23, 2008 12:22 PM
To: FDO Internals Mail List
Subject: RE: [fdo-internals] Counting rows in managed IFeatureReader

Are there any concerns about the number of records changing between the
first SelectAggregates and the Select, or are all providers
transactional across a single session?


-----Original Message-----
From: Robert Fortin
Subject: RE: [fdo-internals] Counting rows in managed IFeatureReader

The 1st select should be a selectaggregate call using function Count()
where it is available.  This will be optimized for most provider, will
avoid a full table scan and will limit the number of trip to the server.
The 2nd is to process those rows as needed.
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