From: | Erik Wienhold <ewie(at)ewie(dot)name> |
---|---|
To: | Loles <lolesft(at)gmail(dot)com>, pgsql-admin(at)postgresql(dot)org |
Subject: | Re: No problem, only curiosity |
Date: | 2023-01-24 13:51:55 |
Message-ID: | 2014960602.121600.1674568315040@office.mailbox.org |
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Lists: | pgsql-admin |
> On 24/01/2023 14:06 CET Loles <lolesft(at)gmail(dot)com> wrote:
>
> Does anyone know why I am getting a result less than 2 million rows in this
> example?
>
> postgres=# create table test_n_tup_live (id serial);
> CREATE TABLE
>
> postgres=# insert into test_n_tup_live select generate_series(1,1000000);
> INSERT 0 1000000
>
> postgres=# analyze test_n_tup_live ;
> ANALYZE
>
> postgres=# select n_live_tup, n_dead_tup from pg_stat_user_tables where relname = 'test_n_tup_live';
>
> n_live_tup | n_dead_tup
> ------------+------------
> 1000000 | 0
> (1 fila)
>
> postgres=# update test_n_tup_live set id = id + 1;
> UPDATE 1000000
>
> postgres=# insert into test_n_tup_live select generate_series(1,1000000);
> INSERT 0 1000000
>
> postgres=# select n_live_tup, n_dead_tup from pg_stat_user_tables where relname = 'test_n_tup_live';
> n_live_tup | n_dead_tup
> ------------+------------
> 2000000 | 1000000
> (1 fila)
>
> postgres=# vacuum test_n_tup_live;
> VACUUM
>
> postgres=# select n_live_tup, n_dead_tup from pg_stat_user_tables where relname = 'test_n_tup_live';
>
> n_live_tup | n_dead_tup
> ------------+------------
> 1999925 | 0
> (1 fila)
Both numbers are estimates: https://www.postgresql.org/docs/current/monitoring-stats.html#MONITORING-PG-STAT-ALL-TABLES-VIEW
--
Erik
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