Interactive report performance problem over database link

Question

Hi gurus,
I have an interactive report that retrieves values from two joined tables both placed on the same remote database. It takes 45 seconds to populate (refresh) a page after issuing a search. If I catch the actual select that is generated by apex ( the one with count(*) over ()...) and run it from sql environment, it takes 1 or 2 seconds. What on earth does consume the rest of the time and how to speed this up? I would like to awoid creating and maintaining local materialized views if possible.
Regards
Samo

Answer 1

Hi
APEX normally needs to return the full result set for the purposes of pagination (where you have it set to something along the lines of show x-y of z), changing this or the max row count can affect performance greatly.
The driving site hint would need to refer to the name of the view, but can be a bit temperamental with this kind of thing. The materialize hint only works for sub-factored queries (in a 'WITH blah AS(SELECT /*+ MATERIALIZE */ * FROM etc. etc.)). They tend to materialize anyway and its best not to use hints like that for production code unless there is absolutely no other option, but just sub factoring without hints can often have a profound effect on performance. For instance
WITH a AS
SELECT c1,
        c2,
        c3,
        c4,
        c5
FROM schema1.view1)
, b AS
SELECT c1,
        c2,
        c3
FROM schema1.view2)
SELECT *
FROM a, b
WHERE a.c5 = b.c3May produce a different plan or even just sub factoring one of the external tables may have an effect.
You need to try things out here and experiment and keep looking at the execution plans. You should also change Toads row fetch setting to be all 9's to get a real idea of performance.
Let me know how you get on.
Cheers
Ben
http://www.munkyben.wordpress.com
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Edited by: Munky on Sep 29, 2009 1:41 PM