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

From: Alvaro Herrera
Subject: Re: Internal operations when the planner makes a hash join.
Date: ,
Msg-id: 20100223165339.GF3672@alvh.no-ip.org
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In response to: Re: Internal operations when the planner makes a hash join.  (negora)
Responses: Re: Internal operations when the planner makes a hash join.  (Scott Carey)
List: 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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From: negora
Date:
Subject: Re: Internal operations when the planner makes a hash join.
From: "Kevin Grittner"
Date:
Subject: Re: Internal operations when the planner makes a hash join.