Comments on: Joins – NLJ

By: Log Buffer #199, A Carnival of the Vanities for DBAs | The Pythian Blog

Log Buffer #199, A Carnival of the Vanities for DBAs | The Pythian Blog — Sat, 14 Aug 2010 20:53:18 +0000

[...] Lewis started a series about joins. Jonathan is the master of building clear and excellent test cases, and this post is a good example [...]

By: Joins – HJ « Oracle Scratchpad

Joins – HJ « Oracle Scratchpad — Tue, 10 Aug 2010 18:46:28 +0000

[...] Joins – HJ Filed under: CBO,Execution plans,Performance — Jonathan Lewis @ 6:43 pm UTC Aug 10,2010 In the second note on my thesis that “all joins are nested loop joins with different startup costs” I want to look at hash joins, and I’ll start by going back to the execution plan I posted on “Joins – NLJ”. [...]

By: Manish

Manish — Tue, 10 Aug 2010 12:42:44 +0000

Thanks Jonathan.

BTW the db was 10.2.0.4.

By: Timur Akhmadeev

Timur Akhmadeev — Tue, 10 Aug 2010 12:04:24 +0000

>seems to be fixed in 11.2
and in 10.2.0.5 too

By: Jonathan Lewis

Jonathan Lewis — Tue, 10 Aug 2010 09:44:49 +0000

Narenda,

True, I just tried it myself. Even a full google search shows little more than a couple of passing references I’ve made to the feature and lists of hints from 11g. It’s possible that I’m remembering a discussion from Christian’s book. (Troubleshooting Oracle Performance).

By: Narendra

Narendra — Tue, 10 Aug 2010 09:40:00 +0000

Well, Oak Table did not find any entries.
http://www.oaktable.net/search/node/nlj%20batching

By: Jonathan Lewis

Jonathan Lewis — Tue, 10 Aug 2010 09:19:42 +0000

Narenda, I may find some time to comment on this one day. In the meantime, I thought Christian Antognini and Tanel Poder had made various comments on the changes. Search for "nlj_batching" on their web sites, or on the "Oak Table Safe Search".

By: Jonathan Lewis

Jonathan Lewis — Tue, 10 Aug 2010 08:52:48 +0000

Manish,

This isn’t the right place, and you haven’t given a version number.
I’ve reproduced this on 11.1.0.6 – the first query erroneously returns two rows, the second correctly returns none – it’s a bug, raise an SR.

Looking at the 10053, Oracle seems to have “lost” the sal > null predicate in part of the logic for calculating single table cardinalities in the case where that predicate is the last for the table. The error doesn’t occur if the null is supplied as a bind variable.

By: Sokrates

Sokrates — Tue, 10 Aug 2010 08:41:27 +0000

Manish,

this is a bug (I can reproduce it in 10.2, seems to be fixed in 11.2)
TRUE and UNKNOWN : UNKNOWN
UNKNOWN and TRUE : UNKNOWN

see
http://download.oracle.com/docs/cd/B19306_01/server.102/b14200/conditions004.htm#i1052219
http://download.oracle.com/docs/cd/E11882_01/server.112/e10592/conditions004.htm#i1052219

By: Narendra

Narendra — Tue, 10 Aug 2010 08:25:40 +0000

Jonathan,

As you have written specifically about Nested Loop Joins, would it be possible for you to mention how oracle processes NL join, especially in following releases?
a) 8i (plan as mentioned above)
b) 9i and 10g (introduced table prefetch)
c) 11g (don’t know what it is called but plan changes a bit)
I have not managed to find these details in a single document/post anywhere else.