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Re: Internal operations when the planner makes a hash join.

From: Alvaro Herrera <alvherre(at)commandprompt(dot)com>
To: negora <negora(at)negora(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Internal operations when the planner makes a hash join.
Date: 2010-02-23 16:53:39
Message-ID: 20100223165339.GF3672@alvh.no-ip.org (view raw or flat)
Thread:
Lists: pgsql-performance
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.

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