Details
-
Bug
-
Status: Closed (View Workflow)
-
Major
-
Resolution: Fixed
-
None
-
None
-
None
Description
I used DBT-3 data, scale=10, InnoDB engine. I create statistical tables like
specified in scripts/mysql_system_tables.sql.
Then I use the following to generate the histogram:
MariaDB [dbt3sf10]> set histogram_size=200;
|
Query OK, 0 rows affected (0.00 sec)
|
|
|
MariaDB [dbt3sf10]> set histogram_type='single_prec_hb';
|
Query OK, 0 rows affected (0.00 sec)
|
MariaDB [dbt3sf10]> analyze table customer persistent for all;
|
Then I want to take a look at the histogram:
MariaDB [dbt3sf10]> select *,hex(histogram),length(histogram) from mysql.column_stats where column_name='c_acctbal' and table_name='customer'\G
|
*************************** 1. row ***************************
|
db_name: dbt3sf10
|
table_name: customer
|
column_name: c_acctbal
|
min_value: -999.99
|
max_value: 9999.99
|
nulls_ratio: 0.0000
|
avg_length: 8.0000
|
avg_frequency: 1.8319
|
hist_size: 200
|
hist_type:
|
histogram: ���
|
������� "%'),.0357:<>ACEHJLOQSVXZ\_acfhjmoqtvx{}������������������������������������������������������ � �
|
�P � �? �w��� � mmen
|
hex(histogram): 020406090B0D10121417191B1E20222527292C2E303335373A3C3E414345484A4C4F515356585A5C5F616366686A6D6F717476787B7D7F828486898B8D90929497999B9EA0A2A5A7A9ACAEB0B2B5B7B9BCBEC0C3C5C7CACCCED1D3D5D8DADCDFE1E3E6E8EAEDEFF1F4F6F8FBFD00000001000000000000000300000000000000000000000B00000003500000000000000100000000000000000000000000F03F00000000000000000000000000000000F0770298C67F00000000000000000000010000006D6D656E
|
Look at the hex(histogram) data. The first half of it has growing values:
02,04,06,09,0B,0D, ..., F1,F4,F6,F8,FB,FD.. Then it goes back to zero, and
continues at zero, with a few spikes.
As far as I understand the meaning of values in a histogram, they should always
increase. That is, histogram[i+1] >= histogram[i]. This is not the case for
this histogram.
Attachments
Issue Links
- relates to
-
MDEV-4145 Take into account the selectivity of single-table range predicates on non-indexed columns when searching for the best execution plan
-
- Closed
-