[Qgis-developer] Oracle layers - improving the speed

Jonathan Moules jonathanmoules at warwickshire.gov.uk
Tue Feb 4 09:54:10 PST 2014

Hi List,
The native Oracle provider has been in QGIS for quite a while (a year?) and
is generally quite good.

However there are still two fundamental issues that we have with it, both
as a result of the fact that Oracle doesn't store accurate spatial metadata:

a) Whenever I "Connect" to the Oracle database, QGIS performs a scan of
every table to get the metadata which can take almost 2 minutes (the
results are cached by Oracle and subsequent "Connects" are faster, but only
for an hour or two). This is using the "Only look in metadata table", "use
estimated table metadata" and "only existing geomtetry types" checkboxes.
See also - http://hub.qgis.org/issues/8689

b) When I add a specific Oracle table, QGIS then performs some checks
against it (I believe trying to find the actual BBOX). This is fine for
small tables, but for large tables it can take several minutes for the
layer to get added - locking up QGIS in the interim - even if "render" is
The issue becomes even more problematical when re-opening a project - QGIS
then rescans all of the tables included in the project which can mean a
several minute delay after opening the project.

None of the other GIS-y systems we have have this problem. ArcMap and
MapInfo solve it by having their own metadata tables that we have to
manually maintain :-( . FME solves it by... well I don't know how (not
separate metadata tables).

So my question is - is there any development work that can be done on the
QGIS end to speed either of these things up? Ticket 8689 linked above has a
couple of my thoughts, but I'm sure the list can come up with better

Any thoughts? Particularly item (b). We're willing to consider sponsoring
these particular changes as we're heavy Oracle users, hence me asking. :-)


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