[#MDEV-4369] column_stats.histogram contents doesnt make sense

I used DBT-3 data, scale=10, InnoDB engine. I create statistical tables like
specified in scripts/mysql_system_tables.sql.

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;

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.

[MDEV-4369] column_stats.histogram contents doesnt make sense Created: 2013-04-04 Updated: 2013-04-07 Resolved: 2013-04-07
Status:	Closed
Project:	MariaDB Server
Component/s:	None
Affects Version/s:	None
Fix Version/s:	None

[MDEV-4369] column_stats.histogram contents doesnt make sense Created: 2013-04-04 Updated: 2013-04-07 Resolved: 2013-04-07