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.
Date: Tue, 23 Feb 2010 13:53:39 -0300
Message-ID: <20100223165339.GF3672@alvh.no-ip.org> (raw)
In-Reply-To: <4B8404CC.4060607@negora.com>
References: <4B83E8C5.2050902@negora.com>
<4B83A03E020000250002F4FD@gw.wicourts.gov>
<4B8404CC.4060607@negora.com>
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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To: pgsql-performance@postgresql.org
Cc: alvherre@commandprompt.com, negora@negora.com
Subject: Re: Internal operations when the planner makes a hash join.
In-Reply-To: <20100223165339.GF3672@alvh.no-ip.org>
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