Hi Jürgen,
After your remarks I thought I would try the individual update
statements (7000 of them ) directly on postgres. Indeed, that gives an
out of memory error after 10 minutes. Not sure if that is entirely up to
the expensive view or that there is something more going on. I also
tried writing the update statement as an update on the view with the
where clause being 'where id in (list of ids)', this again goes quickly
(6 seconds).
To sum it up: unless there is a way in QGIS to update selections using
one update statement with a where clause (as opposed to individual
update statements per record), it is not possible to work with larger
selections on 'expensive' views in postgres. Would that be difficult to
implement, or are there other reasons for issuing individual statements?
Thanks again all for your thoughts,
Janneke
On 29/11/2015 22:36, Jürgen E. Fischer wrote:
Hi Janneke,
On Sun, 29. Nov 2015 at 20:44:54 +0300, Janneke van Dijk wrote:
Using the field calculator either from the attribute table or from main
window with the attribute table closed both takes too long to be useful. Not
the actual calculation, but the saving of the edits. To be clear: I
originally used the update expression bar to update the selection, but all
three methods take too long to save.
That's because - as Matthias already said - the expression are evaluated for
each record and the changed attribute value is temporary stored in QGIS. When
you commit the changed records are iterated and a separate UPDATE statements is
issued for each record. And that's what takes long - although an expensive
view contributes to the time each UPDATE needs.
The comment about the attribute table was just because for each change also the
attribute table(s) UI is updated. So execution might be quicker if there are
no open attribute tables. But the actual updates should perform the same from
wherever you invoke the feature calculator.
Jürgen
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