Re: how does oracle manage hash maps?

From: Jonathan Lewis <jonathan_at_jlcomp.demon.co.uk>
Date: Fri, 13 Feb 2004 09:38:40 -0000
Message-ID: <009801c3f215$2a511de0$6702a8c0@Primary>

> Traditional hashing uses an array for the hash,
> then a linked list for the collisions.

I believe this is exactly what Oracle does when building the hash table (build table) for a hash join. Bear in mind that all the columns from the hashed data set (select columns and join columns) are copied into the hash table, so any references to the cache buffer are a distraction.

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Original Message ----- From: "Ryan" <ryan.gaffuri_at_cox.net> To: <oracle-l_at_freelists.org> Sent: Friday, February 13, 2004 4:12 AM Subject: how does oracle manage hash maps?

When Oracle performs a hash-join it first creates a hashmap. This hash map is placed in the PGA. Now, Oracle uses linked lists to manage the buffer cache. Traditional hashing uses an array for the hash, then a linked list for the collisions. How does Oracle manage this?

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Received on Fri Feb 13 2004 - 03:38:40 CST