Message-ID: <429B8D05.5040705@PresiNET.com>
Date: Mon, 30 May 2005 15:00:37 -0700
From: Bricklen Anderson <BAnderson@PresiNET.com>
User-Agent: Debian Thunderbird 1.0.2 (X11/20050331)
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To: Colton A Smith <smith@cs.utk.edu>
Cc: pgsql-performance@postgresql.org
Subject: Re: poor performance involving a small table
References: <Pine.GSO.4.62.0505261052180.25866@hydra3>
In-Reply-To: <Pine.GSO.4.62.0505261052180.25866@hydra3>
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Colton A Smith wrote:
> 
> Hi:
> 
>  I have a table called sensors:
> 
>                                     Table "public.sensor"
>      Column      |           Type           |                    Modifiers
> -----------------+--------------------------+------------------------------------------------- 
> 
>  sensor_id       | integer                  | not null default 
> nextval('sensor_id_seq'::text)
>  sensor_model_id | integer                  | not null
>  serial_number   | character varying(50)    | not null
>  purchase_date   | timestamp with time zone | not null
>  variable_id     | integer                  | not null
>  datalink_id     | integer                  | not null
>  commentary      | text                     |
> Indexes:
>     "sensor_pkey" PRIMARY KEY, btree (sensor_id)
> Foreign-key constraints:
>     "datalink_id_exists" FOREIGN KEY (datalink_id) REFERENCES 
> datalink(datalink_id) ON DELETE RESTRICT
>     "sensor_model_id_exists" FOREIGN KEY (sensor_model_id) REFERENCES 
> sensor_model(sensor_model_id) ON DELETE RESTRICT
>     "variable_id_exists" FOREIGN KEY (variable_id) REFERENCES 
> variable(variable_id) ON DELETE RESTRICT
> 
> 
> Currently, it has only 19 rows.  But when I try to delete a row, it takes
> forever.  I tried restarting the server.  I tried a full vacuum to no 
> avail.  I tried the following:
> 
> explain analyze delete from sensor where sensor_id = 12;
>                                            QUERY PLAN
> ------------------------------------------------------------------------------------------------ 
> 
>  Seq Scan on sensor  (cost=0.00..1.25 rows=1 width=6) (actual 
> time=0.055..0.068 rows=1 loops=1)
>    Filter: (sensor_id = 12)
>  Total runtime: 801641.333 ms
> (3 rows)
> 
> Can anybody help me out?  Thanks so much!
> 

I'd say the obvious issue would be your foreign keys slowing things down. Have 
you analyzed the referenced tables, and indexed the columns on the referenced 
tables?

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