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Re: Innodb_buffer_pool_read_requests is zero

 

Hi,

The INNODB_METRICS are partly duplicating global status variables. I
would actually like to remove them eventually; see
https://jira.mariadb.org/browse/MDEV-15706. This interface was
designed in MySQL before performance_schema was developed. I do not
know if the author considered using status variables.

The regressions that you found were not intentional; we should avoid
changing interfaces within GA releases such as 10.6. The only
intentional change was to remove some "double bookkeeping" and let
some INNODB_METRICS counters reflect counters that are already being
maintained for other reasons, instead of duplicating them.

Some indirection for the counter Innodb_buffer_pool_read_requests was
removed in MDEV-26827: the duplicate global variable
export_vars.innodb_buffer_pool_read_requests was removed and the
status variable should reflect buf_pool.stat.n_page_gets directly.
When diagnosing https://jira.mariadb.org/browse/MDEV-29967 I did see
that counter being incremented. The statement that I used was:

show global status like 'innodb_buffer_pool_read%';

Can you please file a bug with exact steps on how to reproduce this?

Marko

On Fri, May 12, 2023 at 10:12 AM <mariadb@xxxxxxxxxxxxxx> wrote:
>
> Figured out trx_rseg_history_len; it's just disabled by default now. But
> still stumped on Innodb_buffer_pool_read_requests.
>
> On 5/12/2023 2:40 AM, mariadb@xxxxxxxxxxxxxx wrote:
> > I've also noticed that my transaction history length is always zero;
> > that's true on all my 10.6.13 instances (not just Bullseye). Is that
> > information no longer stored here?
> >
> > SELECT `count` FROM information_schema.INNODB_METRICS WHERE name =
> > 'trx_rseg_history_len';
> >
> > On 5/11/2023 11:55 PM, mariadb@xxxxxxxxxxxxxx wrote:
> >> Just upgraded from 10.6.12 to 10.6.13 on a Debian Bullseye system, and
> >> seeing this oddity. Innodb_buffer_pool_read_requests is zero, and
> >> seems to remain at zero no matter what I do (I even tried selecting
> >> all the data from a small table several times in a row with no
> >> change). It's been running a couple hours now; I've restarted it a
> >> couple times. I have 10.6.13 on a few other platforms as well
> >> (including Buster), and I'm not seeing the same issue on them. What
> >> would cause this? I have no other Bullseye systems running 10.6.13
> >> yet, and the same system has been running 10.6.12 for over a week now
> >> without showing this issue.
> >>
> >> The system _seems_ to be running fine, it's a replica system that is
> >> being fed actively from the master (data comes in to it very regularly).
> >>
> >> MariaDB [(none)]> SHOW GLOBAL STATUS LIKE 'innodb_buffer_pool_%';
> >> +-----------------------------------------+--------------------------------------------------+
> >> | Variable_name                           | Value                     |
> >> +-----------------------------------------+--------------------------------------------------+
> >> | Innodb_buffer_pool_dump_status          |                     |
> >> | Innodb_buffer_pool_load_status          | Buffer pool(s) load
> >> completed at 230511 23:21:26 |
> >> | Innodb_buffer_pool_resize_status        |                     |
> >> | Innodb_buffer_pool_load_incomplete      | OFF                     |
> >> | Innodb_buffer_pool_pages_data           | 609103                     |
> >> | Innodb_buffer_pool_bytes_data           | 9979543552
> >>                      |
> >> | Innodb_buffer_pool_pages_dirty          | 19465                     |
> >> | Innodb_buffer_pool_bytes_dirty          | 318914560
> >>                     |
> >> | Innodb_buffer_pool_pages_flushed        | 0                     |
> >> | Innodb_buffer_pool_pages_free           | 299441                     |
> >> | Innodb_buffer_pool_pages_made_not_young | 0                     |
> >> | Innodb_buffer_pool_pages_made_young     | 107                     |
> >> | Innodb_buffer_pool_pages_misc           | 0                     |
> >> | Innodb_buffer_pool_pages_old            | 224824                     |
> >> | Innodb_buffer_pool_pages_total          | 908544                     |
> >> | Innodb_buffer_pool_pages_lru_flushed    | 0                     |
> >> | Innodb_buffer_pool_pages_lru_freed      | 0                     |
> >> | Innodb_buffer_pool_pages_split          | 726                     |
> >> | Innodb_buffer_pool_read_ahead_rnd       | 0                     |
> >> | Innodb_buffer_pool_read_ahead           | 3                     |
> >> | Innodb_buffer_pool_read_ahead_evicted   | 0                     |
> >> | Innodb_buffer_pool_read_requests        | 0                     |
> >> | Innodb_buffer_pool_reads                | 604346                     |
> >> | Innodb_buffer_pool_wait_free            | 0                     |
> >> | Innodb_buffer_pool_write_requests       | 3639341                     |
> >> +-----------------------------------------+--------------------------------------------------+
> >> 25 rows in set (0.000 sec)
> >>
> >> MariaDB [(none)]> SHOW VARIABLES LIKE 'innodb_buffer_pool%';
> >> +-------------------------------------+----------------+
> >> | Variable_name                       | Value          |
> >> +-------------------------------------+----------------+
> >> | innodb_buffer_pool_chunk_size       | 134217728      |
> >> | innodb_buffer_pool_dump_at_shutdown | ON             |
> >> | innodb_buffer_pool_dump_now         | OFF            |
> >> | innodb_buffer_pool_dump_pct         | 80             |
> >> | innodb_buffer_pool_filename         | ib_buffer_pool |
> >> | innodb_buffer_pool_load_abort       | OFF            |
> >> | innodb_buffer_pool_load_at_startup  | ON             |
> >> | innodb_buffer_pool_load_now         | OFF            |
> >> | innodb_buffer_pool_size             | 15032385536    |
> >> +-------------------------------------+----------------+
> >> 9 rows in set (0.000 sec)
> >>
> >> _______________________________________________
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> >
> > _______________________________________________
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> >
>
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-- 
Marko Mäkelä, Lead Developer InnoDB
MariaDB plc


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