Join performance - Mailing list pgsql-performance

From Pierre-Frédéric Caillaud
Subject Join performance
Date
Msg-id opsbuw6yr5cq72hf@musicbox
Whole thread Raw
In response to Re: best way to fetch next/prev record based on index  ("Merlin Moncure" <merlin.moncure@rcsonline.com>)
List pgsql-performance
    Hello,

    I'm building a kind of messaging/forum application with postgresql. There
are users which will send each others messages, send messages to forums,
etc.
    I would like to put the messages in folders, so each user has several
folders (inbox, sent...), and forums are also folders.

    A message will appear in the sender's "sent" folder and the receiver's
inbox, or receiving forum folder.

    There are two ways I can do this :
    - either by placing two folder fields (outbox_folder_id and
receiving_folder_id) in the messages table, which can both point to a
folder or be null. When a user sends a message to another user/folder,
these fields are set appropriately.
    - or by having a messages table, and a link table linking messages to
folders.

    I have built a test database with about 20000 messages in 2000 folders
(10 messages per folder).

    Finding all the messages in a folder takes more than 600 times longer
with the link table than with the single table approach (66 ms vs. 0.12
ms).

    Is this normal ? I have checked explain analyze and it uses indexes in
all cases. The query plans look right to me.


pgsql-performance by date:

Previous
From: Greg Stark
Date:
Subject: Re: best way to fetch next/prev record based on index
Next
From: Tom Lane
Date:
Subject: Re: best way to fetch next/prev record based on index