Comments on: Operation CONNECT BY WITH FILTERING

By: Resolving chains of events with CONNECT_BY « Todor Botev's Blog

Resolving chains of events with CONNECT_BY « Todor Botev's Blog — Sun, 23 Aug 2009 07:26:02 +0000

[...] of data. So please test for performance – with a data volume comparable to the real one. Here is a very good detailed explanation by Christian Antognini of how CONNECT_BY is executed internally [...]

By: Christian Antognini

Christian Antognini — Fri, 17 Jul 2009 13:44:40 +0000

Hi Todor

Sorry, but I don’t know why this double check is needed. My best guess is the following: since it is an access predicate (not a filter predicate), this probably means that data is placed in a memory structure (kind-of hash table) and, to access it, the key is MGR.

Cheers,
Chris

By: Todor Botev

Todor Botev — Thu, 02 Jul 2009 10:50:30 +0000

Thank you for this insightfull and very well written post!

[...]9. Operation 1 applies the access predicate “MGR”=PRIOR “EMPNO” and sends the 14 rows to the caller.[...]

Why do we need the access predicate in operation 1 ? I think the whole algorithm ensures that only “valid” rows get reported to operation 1. Why is it needed to apply the predicate once more before sending them to the caller?

By: Alen

Alen — Tue, 30 Jun 2009 12:08:04 +0000

I’ve been always wondering what is that third child operation which always shows “table access full” and never gets executed. Finally I got the answer!

By: Connect By « Oracle Scratchpad

Connect By « Oracle Scratchpad — Tue, 30 Jun 2009 09:22:24 +0000

[...] an interesting post on this topic on Christian Antognini’s blog (which I’ve also referenced from the OTN posting) [...]

By: Rudy

Rudy — Mon, 22 Jun 2009 07:50:49 +0000

Thank you for reporting this. I very likely hit this bug and verified it has been fixed in patch set 3.
Bye :-)

By: Alex Shea

Alex Shea — Thu, 02 Oct 2008 21:01:21 +0000

Christian, thanks for this helpful page. I was at my wit’s end trying to speed up an 86 line
connect-by query that takes 3 hour to finish on a 10.2.0.1. THANKS for mentioning that it is a bug.