Re: Slow query on V12.

Em 23/09/2019 16:03, Luís Roberto Weck escreveu:
> Em 23/09/2019 15:43, nikhil raj escreveu:
>> Hi,
>>
>> Can you check by vacuum analyze  the database. And run the query.
>>
>>
>> **Remember don't  use Vacuum full.
>>
>> On Tue, 24 Sep 2019, 12:07 am Luís Roberto Weck, 
>> <[email protected] <mailto:[email protected]>> wrote:
>>
>>     Hi!
>>
>>     Recently I've been looking for bloat in my databases and found a
>>     query to show which tables are more bloated and by how much.
>>
>>     This is the explain plan on v12.3: https://explain.depesz.com/s/8dW8C
>>     And this is with v11: https://explain.depesz.com/s/diXY
>>
>>     Both databases have approx. the same size and have the same
>>     schema, but on v12 I the query takes much longer to run.
>>
>>
> Hi!
>
> Thanks for the reply!
>
> Here's the plan after running vacuum analyze: 
> https://explain.depesz.com/s/lhcl
>
> There was no difference in execution time.

This is the query that is actually slow:

-- EXPLAIN (ANALYZE, COSTS, VERBOSE, BUFFERS)
SELECT table_schema, table_name,
        n_live_tup::numeric as est_rows,
        pg_table_size(relid)::numeric as table_size
   FROM information_schema.columns
        JOIN pg_stat_user_tables as psut ON table_schema = 
psut.schemanameAND table_name = psut.relname
        LEFT JOIN pg_statsON table_schema = pg_stats.schemanameAND 
table_name = pg_stats.tablenameAND column_name = attname
  WHERE attname IS NULL
    AND table_schema NOT IN ('pg_catalog', 'information_schema')
  GROUP BY table_schema, table_name, relid, n_live_tup

If I turn the left join to a inner join, the query runs very fast.

Plans:
  LEFT JOIN: https://explain.depesz.com/s/i88x
  INNER JOIN: https://explain.depesz.com/s/ciSu

Ofcourse, that's not what the full query needs