Re: Re: how does oracle manage hash maps?
- From: "Jonathan Lewis" <jonathan@xxxxxxxxxxxxxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Fri, 13 Feb 2004 14:06:35 -0000
The relevant subset of data values gets copied
into the hash map. That means the rows and
columns required from the table, not the whole
table.
You might be interested doing a hash join
with event 10104 set - level 12 is an option
with Oracle 9, otherwise just:
alter session set events '10104 trace name context forever';
execute query that does one hash join.
alter session set events '10104 trace name context off';
You'll probably recognise references to all
the bits you would expect to see.
Regards
Jonathan Lewis
http://www.jlcomp.demon.co.uk
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who can answer the questions, but the
person who can question the answers -- T. Schick Jr
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----- Original Message -----
From: <ryan.gaffuri@xxxxxxx>
To: <oracle-l@xxxxxxxxxxxxx>
Sent: Friday, February 13, 2004 1:57 PM
Subject: Re: Re: how does oracle manage hash maps?
I know how the LRU works with linked lists. I've written linked list code
before.
From your diagram I take it that, oracle builds the hash map in the pga. The
number of buckets is a prime number.
Its hard to read your diagram. I'm not quite sure how the hash map links to
the buffer chain. In basic hashing methodology each hash bucket points to a
specific value.
Jonathan lewis stated that in making the hash map oracle grabs the actually
values you want to return. However, those values don't go into the PGA with
the hash map do they? I thought all data elements went into the buffer
cache?
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