Chapter 9, page 33 - Cat-Hash-strophes
in the seminar notes. (The page number
may have changed a little).
If you have a plan like this, all the leading
tables have been hashed into memory at
the same time.
HASH JOIN
TABLE ACCESS (FULL) OF TABLE_4
HASH JOIN
TABLE ACCESS (FULL) OF TABLE_3
HASH JOIN
TABLE ACCESS (FULL) OF TABLE_2
TABLE ACCESS (FULL) OF TABLE_1
It is true that Oracle only works out the cost of joining
two objects at a time - but the actual execution can pass
results from stage to step before a step is completed,
just like the NL join.
In this example, the 10053 trace showed (if I recall
correctly):
calc 1: join t2 to t1 with swap_join_inputs
calc2: join t3 to result1 with swap_join_inputs
calc3: join t4 to result2 with swap_join_inputs
Regards
Jonathan Lewis
http://www.jlcomp.demon.co.uk
The educated person is not the person
who can answer the questions, but the
person who can question the answers -- T. Schick Jr
One-day tutorials:
http://www.jlcomp.demon.co.uk/tutorial.html
Three-day seminar:
see http://www.jlcomp.demon.co.uk/seminar.html
____UK___November
The Co-operative Oracle Users' FAQ
http://www.jlcomp.demon.co.uk/faq/ind_faq.html
----- Original Message -----
To: "Multiple recipients of list ORACLE-L" <[EMAIL PROTECTED]>
Sent: Wednesday, December 31, 2003 12:19 AM
> I've alway understood that joining occurs always in two steps, first two
> tables, then their result (row source) with next table and so on, so
there's
> no need for more than 2 hash tables for example?
>
> Tanel.
>
--
Please see the official ORACLE-L FAQ: http://www.orafaq.net
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Author: Jonathan Lewis
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