Re: Slow query on V12.

[Luís Roberto Weck <luisroberto@xxxxxxxxxxxxxxx>]

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, <luisroberto@xxxxxxxxxxxxxxx> 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.schemaname AND table_name = psut.relname
       LEFT JOIN pg_stats ON table_schema = pg_stats.schemaname AND table_name = pg_stats.tablename AND 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