Details
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Bug
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Status: Closed (View Workflow)
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Major
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Resolution: Fixed
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10.4(EOL)
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None
Description
So after MDEV-15253 and co., the default settings in 10.4 are:
mysql> show variables like 'use_%';
|
+-----------------+------------------------+
|
| Variable_name | Value |
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+-----------------+------------------------+
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| use_stat_tables | PREFERABLY_FOR_QUERIES |
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+-----------------+------------------------+
|
mysql> show variables like 'optimizer_us%';
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+-------------------------------------+-------+
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| Variable_name | Value |
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+-------------------------------------+-------+
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| optimizer_use_condition_selectivity | 4 |
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+-------------------------------------+-------+
|
mysql> show variables like 'hist%';
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+----------------+----------------+
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| Variable_name | Value |
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+----------------+----------------+
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| histogram_size | 0 |
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| histogram_type | SINGLE_PREC_HB |
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+----------------+----------------+
|
Create a table and fill with some data
create table ten(a int); |
insert into ten values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9); |
 |
create table one_k(a int); |
insert into one_k select A.a + B.a* 10 + C.a * 100 from ten A, ten B, ten C; |
create table t1 (a int, b int); |
insert into t1 select A.a+100*B.a, A.a+1000*B.a from one_k A, one_k B; |
Then
mysql> analyze table t1;
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+---------+---------+----------+----------+
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| Table | Op | Msg_type | Msg_text |
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+---------+---------+----------+----------+
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| test.t1 | analyze | status | OK |
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+---------+---------+----------+----------+
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1 row in set (0.03 sec)
|
This is instant as it used to be. Good.
mysql> analyze table t1 persistent for all;
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+---------+---------+----------+-----------------------------------------+
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| Table | Op | Msg_type | Msg_text |
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+---------+---------+----------+-----------------------------------------+
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| test.t1 | analyze | status | Engine-independent statistics collected |
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| test.t1 | analyze | status | OK |
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+---------+---------+----------+-----------------------------------------+
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2 rows in set (11.92 sec)
|
This collects EITS stats. It takes a while. Debugging, one can see that a Unique object is constructed and filled with data.
But the histogram is not created, which is logical as the setting is that histogram_size=0.
mysql> select * from mysql.column_stats;
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+---------+------------+-------------+-----------+-----------+-------------+------------+---------------+-----------+-----------+-----------+
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| db_name | table_name | column_name | min_value | max_value | nulls_ratio | avg_length | avg_frequency | hist_size | hist_type | histogram |
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+---------+------------+-------------+-----------+-----------+-------------+------------+---------------+-----------+-----------+-----------+
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| test | t1 | a | 0 | 100899 | 0.0000 | 4.0000 | 9.9108 | 0 | NULL | NULL |
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| test | t1 | b | 0 | 999999 | 0.0000 | 4.0000 | 1.0000 | 0 | NULL | NULL |
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+---------+------------+-------------+-----------+-----------+-------------+------------+---------------+-----------+-----------+-----------+
|
The point of this MDEV is that default histogram size/ type should specify a value which does cause histogram to be collected.
Attachments
Issue Links
- relates to
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MDEV-15253 Default optimizer setting changes for MariaDB 10.4
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- Closed
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