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Date: Tue, 23 Feb 2010 13:53:39 -0300
From: Alvaro Herrera <alvherre@commandprompt.com>
To: negora <negora@negora.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Internal operations when the planner makes a hash
 join.
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negora wrote:

> According to how I understood the process, the engine would get the
> name from the student with ID 1 and would look for the name of the
> father with ID 1 in the hashed table. It'd do exactly the same with the
> student #2 and father #2. But my big doubt is about the 3rd one
> (Anthony). Would the engine "know" that it already had retrieved the
> father's name for the student 1 and would avoid searching for it into
> the hashed table (using some kind of internal mechanism which allows to
> "re-utilize" the name)? Or would it search into the hashed table again?<br>

The hash table is searched again.  But that's fast, because it's a hash
table.

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.