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From: Ilia Evdokimov <[email protected]>
To: Alena Rybakina <[email protected]>
To: pgsql-hackers <[email protected]>
Cc: jian he <[email protected]>
Cc: Alexander Korotkov <[email protected]>
Cc: Andrei Zubkov <[email protected]>
Cc: Alena Rybakina <[email protected]>
Cc: [email protected]
Subject: Re: Vacuum statistics
Date: Thu, 7 Nov 2024 17:49:23 +0300
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
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On 22.10.2024 22:30, Alena Rybakina wrote:
>
> Hi!
>
> On 16.10.2024 14:01, Alena Rybakina wrote:
>>>
>>> Thank you for rebasing.
>>>
>>> I have noticed that when I create a table or an index on this table, 
>>> there is no information about the table or index in 
>>> pg_stat_vacuum_tables and pg_stat_vacuum_indexes until we perform a 
>>> VACUUM.
>>>
>>> Example:
>>>
>>> CREATE TABLE t (i INT, j INT);
>>> INSERT INTO t SELECT i/10, i/100 FROM GENERATE_SERIES(1,1000000) i;
>>> SELECT * FROM pg_stat_vacuum_tables WHERE relname = 't';
>>> ....
>>> (0 rows)
>>> CREATE INDEX ON t (i);
>>> SELECT * FROM pg_stat_vacuum_indexes WHERE relname = 't_i_idx';
>>> ...
>>> (0 rows)
>>>
>>> I can see the entries after running VACUUM or executing 
>>> autovacuum. or when autovacuum is executed. I would suggest adding a 
>>> line about the relation even if it has not yet been processed by 
>>> vacuum. Interestingly, this issue does not occur with 
>>> pg_stat_vacuum_database:
>>>
>>> CREATE DATABASE example_db;
>>> SELECT * FROM pg_stat_vacuum_database WHERE dbname = 'example_db';
>>> dboid |       dbname | ...
>>>  ...      | example_db | ...
>>> (1 row)
>>>
>>> BTW, I recommend renaming the view pg_stat_vacuum_database to 
>>> pg_stat_vacuum_database_S_  for consistency with 
>>> pg_stat_vacuum_tables and pg_stat_vacuum_indexes
>>>
>> Thanks for the review. I'm investigating this. I agree with the 
>> renaming, I will do it in the next version of the patch.
>>
> I fixed it. I added the left outer join to the vacuum views and for 
> converting the coalesce function from NULL to null values.
>
> I also fixed the code in getting database statistics - we can get it 
> through the existing pgstat_fetch_stat_dbentry function and fixed 
> couple of comments.
>
> I attached a diff file, as well as new versions of patches.
>
> -- 
> Regards,
> Alena Rybakina
> Postgres Professional

Thank you for fixing it.

1) I have found some typos in the test output files (out-files) when 
running 'make check' and 'make check-world'. These typos might cause 
minor discrepancies in test results. You may already be aware of them, 
but I wanted to bring them to your attention in case they haven't been 
noticed. I believe these can be fixed quickly.

2) Additionally, I observed that when we create a table and insert some 
rows, executing the VACUUM FULL command does not update the information 
in the 'pg_stat_get_vacuum_tables' However, running the VACUUM command 
does update this information as expected. This seems inconsistent, and 
it might be a bug.

Example:
CREATE TABLE t (i INT, j INT) WITH (autovacuum_enabled = false);
INSERT INTO t SELECT i/10, i/100 FROM  GENERATE_SERIES(1,1000000) i;
SELECT * FROM pg_stat_get_vacuum_tables WHERE relname = 't';
schema | relname |    relid | total_blks_read | .........
-----------+------------+---------+----------------------+---------
    public | t            | 21416 |                       0 | ......
(1 row)

VACUUM FULL;
SELECT * FROM pg_stat_get_vacuum_tables WHERE relname = 't';
schema | relname |    relid | total_blks_read | .........
-----------+------------+---------+----------------------+---------
    public | t            | 21416 |                       0 | ......
(1 row)

VACUUM;
SELECT * FROM pg_stat_get_vacuum_tables WHERE relname = 't';
schema | relname |    relid | total_blks_read | .........
-----------+------------+---------+----------------------+---------
    public | t            | 21416 |                 4425 | ......
(1 row)

Regards,
Ilia Evdokimov,
Tantor Labs LLC.

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