RE: HASH_JOIN on RBO?

Hi Chuck,

Your hint is in the wrong position. It should come after the INSERT, not the SELECT. Although the insert and the select are optimized separately, they are treated as a single statement block so far as determining an optimization approach is concerned. Therefore a RULE hint needs to be placed after the first keyword in that statement to be effective.

I have just checked the documentation on this, and unfortunately it is not very helpful. The Oracle8i Tuning guide even says, "A statement block can have only one comment containing hints. This comment can only follow the SELECT, UPDATE, or DELETE keyword." which suggests that you cannot put a hint after an INSERT keyword at all. Of course, you can and you sometimes must.

@ Regards,
@ Steve Adams
@ http://www.ixora.com.au/
@ http://www.christianity.net.au/
@
@ Going to OpenWorld?
@ Catch the Ixora performance tuning seminar too!
@ See http://www.ixora.com.au/seminars/ for details.

-----Original Message-----
From: Chuck Hamilton [mailto:chuck_hamilton_at_yahoo.com] Sent: Thursday, 14 September 2000 2:19
To: Steve Adams
Subject: RE: HASH_JOIN on RBO?

The really odd thing is that the init.ora file has optimizer_mode = RULE. Here's the SQL. It's pretty simple...

INSERT INTO PS_QVC_FAST_SEC
SELECT --+ RULE
A.*
FROM PS_QVC_PERS_SRCH_VW A,
     PS_QVC_QUERY_USERS B
WHERE A.OPRID=B.OPRCLASS; The view it references (PA_QVC_PERS_SRCH_VW) has no hints at all in it's definition. I'm still perplexed by this one.

  Steve Adams <steve.adams_at_ixora.com.au> wrote:

Hi Chuck,

It sounds like there is some syntax error in the hint so that it just has the effect of forcing CBO to be used despite the absence of statistics.

@ Regards,
@ Steve Adams
@ http://www.ixora.com.au/
@ http://www.christianity.net.au/
@
@ Going to OpenWorld?
@ Catch the Ixora performance tuning seminar too!
@ See http://www.ixora.com.au/seminars/ for details.

-----Original Message-----
From: Chuck Hamilton [mailto:chuck_hamilton_at_yahoo.com] Sent: Wednesday, 13 September 2000 7:31
To: Multiple recipients of list ORACLE-L Subject: HASH_JOIN on RBO?

I have a query with a RULE hint, but the execution plan is show hash joins. Is this something new in the 8.1.5 optimizer? It used to be that you could only get HASH joins with CBO. Also, each of the operations is showing a cost and cardinality even though none of the tables have stats. The net result is I'm getting a horrible execution plan that includes Cartesian merges and runs for Received on Wed Sep 13 2000 - 23:44:06 CDT