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Re: EXPLAIN output explanation requested

From: Ron Arts <ron(dot)arts(at)neonova(dot)nl>
To: pgsql-novice(at)postgresql(dot)org
Subject: Re: EXPLAIN output explanation requested
Date: 2008-06-03 17:51:05
Message-ID: 48458489.9080908@neonova.nl (view raw or flat)
Thread:
Lists: pgsql-novice
A. Kretschmer schreef:
> am  Tue, dem 03.06.2008, um 12:35:34 +0200 mailte A. Kretschmer folgendes:
>> I guess, you have much insert/delete or update - operations on this
>> table and no recent vacuum.
>>
>> Try to run a 'vacuum full;' and re-run your query. And, run a 'explain
>> analyse <your query>' to see the estimated costs and the real costs. 
> 
> Btw, run 'select relpages, reltuples from pg_class where relname='phone'; 
> before and after the 'vacuum full' and show us the result.
> 
> 
> Andreas

I did a vacuum without success, but `vacuum full` did the trick:

tium=# select relpages, reltuples from pg_class where relname='phone';
  relpages | reltuples
----------+-----------
     85876 |       658
(1 row)
tium=# vacuum full;
VACUUM
tium=# select relpages, reltuples from pg_class where relname='phone';
  relpages | reltuples
----------+-----------
        17 |       248
(1 row)

tium=# explain analyze select codec1, phonetype from phone;
                                              QUERY PLAN
-----------------------------------------------------------------------------------------------------
  Seq Scan on phone  (cost=0.00..76.77 rows=977 width=11) (actual time=0.007..0.751 rows=248 loops=1)
  Total runtime: 0.957 ms
(2 rows)

tium=#

What do those values relpages and reltuples mean?

Thanks,
Ron


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