MySQL InnoDB whats the difference between Data_Length and Max_Data_Length - mysql

So here is the table status of my test table:
+------+--------+---------+------------+--------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+-------------+------------+-----------------+----------+----------------+---------+
| Name | Engine | Version | Row_format | Rows | Avg_row_length | Data_length | Max_data_length | Index_length | Data_free | Auto_increment | Create_time | Update_time | Check_time | Collation | Checksum | Create_options | Comment |
+------+--------+---------+------------+--------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+-------------+------------+-----------------+----------+----------------+---------+
| TEST | InnoDB | 10 | Compact | 172713 | 1175 | 203096064 | 202309632 | 0 | 5242880 | 181935 | 2015-07-21 23:52:24 | NULL | NULL | utf8_general_ci | NULL | | |
Table is created with:
CREATE TABLE TEST ( id INT(6) UNSIGNED AUTO_INCREMENT PRIMARY KEY, att VARCHAR(1000) NOT NULL);
I heard from some one that Max_data_length used to be a fixed value and it is usually 4gb. But in later version of mysql they change the definition of Max_data_length. So now Max_data_length will grow as you insert more data (just like data_length).
I am wondering whats the new definition of Max_data_length and how is it different from Data_length?
Thanks!
Erben

Related

MySQL "Show table status", auto increment is not correct

I create a new table in Mysql, add some rows, yet the Auto_increment field of show tables still returns NULL.
The mysql manual says: this field should return: "The next Auto_increment value"
https://dev.mysql.com/doc/refman/8.0/en/show-table-status.html
What am I doing wrong?
How can I find the next auto_increment value correctly?
Steps to reproduce:
create table `test` (
`id` int(5) not null auto_increment,
`name` varchar(256),
PRIMARY KEY(`id`)
);
Then I run :
show table status where name like 'test';
Result:
Name, Engine, Version, ..., Auto_increment, ...
'test', 'InnoDB', '10', ..., NULL, ...
Then I run:
insert into test values(null,'name1');
insert into test values(null,'name2');
insert into test values(null,'name3');
Edit: -other insert syntax-
insert into test (name) values('name4');
insert into test (name) values('name5');
insert into test (name) values('name6');
Fetch the status of the table
show table status where name like 'test';
Result
Name, Engine, Version, ..., Auto_increment, ...
'test', 'InnoDB', '10', ..., NULL, ...
Data in the table
select * from test;
Result:
1 name1
2 name2
3 name3
For your information:
SHOW VARIABLES LIKE "%version%";
Result:
'innodb_version', '8.0.12'
'protocol_version', '10'
'slave_type_conversions', ''
'tls_version', 'TLSv1,TLSv1.1,TLSv1.2'
'version', '8.0.12'
'version_comment', 'MySQL Community Server - GPL'
'version_compile_machine', 'x86_64'
'version_compile_os', 'Win64'
'version_compile_zlib', '1.2.11'
edit:
autocommit:
SHOW VARIABLES LIKE "autocommit";
result:
'autocommit', 'ON'
Edit:
After a while it automagically starts working. No clear reason how to make it start working.

It's a feature.. not a bug.
The table statistics are cached. To disable the cache and always have the latest version you should change the server variable that indicates the duration of the cache-clear to 0:
SET PERSIST information_schema_stats_expiry = 0
The default value of this property has changed to 86400 (24 hours) in Mysql 8.x
Example:
SET PERSIST information_schema_stats_expiry = 86400
-- 86400 is the default value of mysql 8.x if you have never changed this you don't need to set this
show variables like 'information_schema_stats_expiry';
+---------------------------------+-------+
| Variable_name | Value |
+---------------------------------+-------+
| information_schema_stats_expiry | 86400 |
+---------------------------------+-------+
create schema mytest;
create table `test` (
`id` int(5) not null auto_increment,
`name` varchar(256),
PRIMARY KEY(`id`)
);
insert into test values(null,'name1')
insert into test values(null,'name2')
insert into test values(null,'name3')
show table status where name like 'test';
+------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+------------+--------------------+----------+----------------+---------+
| Name | Engine | Version | Row_format | Rows | Avg_row_length | Data_length | Max_data_length | Index_length | Data_free | Auto_increment | Create_time | Update_time | Check_time | Collation | Checksum | Create_options | Comment |
+------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+------------+--------------------+----------+----------------+---------+
| test | InnoDB | 10 | Dynamic | 3 | 5461 | 16384 | 0 | 0 | 0 | 4 | 2018-10-09 15:32:15 | 2018-10-09 15:32:16 | NULL | utf8mb4_0900_ai_ci | NULL | | |
+------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+------------+--------------------+----------+----------------+---------+
-- The Auto_increment field is correctly set to 4.. but is now cached.
insert into test values(null,'name3');
show table status where name like 'test';
+------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+------------+--------------------+----------+----------------+---------+
| Name | Engine | Version | Row_format | Rows | Avg_row_length | Data_length | Max_data_length | Index_length | Data_free | Auto_increment | Create_time | Update_time | Check_time | Collation | Checksum | Create_options | Comment |
+------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+------------+--------------------+----------+----------------+---------+
| test | InnoDB | 10 | Dynamic | 3 | 5461 | 16384 | 0 | 0 | 0 | 4 | 2018-10-09 15:32:15 | 2018-10-09 15:32:16 | NULL | utf8mb4_0900_ai_ci | NULL | | |
+------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+------------+--------------------+----------+----------------+---------+
-- The Auto_increment is still 4 (it was cached).
drop schema mytest
Now we change the configuration:
SET PERSIST information_schema_stats_expiry = 0
and we run the same test:
show variables like 'information_schema_stats_expiry'
+---------------------------------+-------+
| Variable_name | Value |
+---------------------------------+-------+
| information_schema_stats_expiry | 0 |
+---------------------------------+-------+
create schema mytest;
create table `test` (
`id` int(5) not null auto_increment,
`name` varchar(256),
PRIMARY KEY(`id`)
);
insert into test values(null,'name1');
insert into test values(null,'name2');
insert into test values(null,'name3');
show table status where name like 'test';
+------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+------------+--------------------+----------+----------------+---------+
| Name | Engine | Version | Row_format | Rows | Avg_row_length | Data_length | Max_data_length | Index_length | Data_free | Auto_increment | Create_time | Update_time | Check_time | Collation | Checksum | Create_options | Comment |
+------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+------------+--------------------+----------+----------------+---------+
| test | InnoDB | 10 | Dynamic | 3 | 5461 | 16384 | 0 | 0 | 0 | 4 | 2018-10-09 15:32:49 | 2018-10-09 15:32:49 | NULL | utf8mb4_0900_ai_ci | NULL | | |
+------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+------------+--------------------+----------+----------------+---------+
-- Auto_increment is 4, but the result is not cached!
insert into test values(null,'name3');
show table status where name like 'test';
+------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+------------+--------------------+----------+----------------+---------+
| Name | Engine | Version | Row_format | Rows | Avg_row_length | Data_length | Max_data_length | Index_length | Data_free | Auto_increment | Create_time | Update_time | Check_time | Collation | Checksum | Create_options | Comment |
+------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+------------+--------------------+----------+----------------+---------+
| test | InnoDB | 10 | Dynamic | 4 | 4096 | 16384 | 0 | 0 | 0 | 5 | 2018-10-09 15:32:49 | 2018-10-09 15:32:49 | NULL | utf8mb4_0900_ai_ci | NULL | | |
+------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+------------+--------------------+----------+----------------+---------+
-- The Auto_increment field is now 5 (a correct, not cached value)
drop schema mytest;

MySQL - i dont see data, but mysql says, that there are rows

I have table ip_per_nat_vlan, innodb format. When I give truncate table, table is empty.
Then I have php script, which fill data into this table.
When is this script finished without errors (simple insert statemets) situation is following:
select * from ip_per_nat_vlan;
Empty set (0.00 sec)
.
select count(*) from ip_per_nat_vlan;
+----------+
| count(*) |
+----------+
| 0 |
+----------+
1 row in set (0.00 sec)
.
show table status;
+----------------------------------+--------+---------+------------+----------+----------------+-------------+-----------------+--------------+------------+----------------+---------------------+---------------------+------------+-----------------+----------+----------------+---------+
| Name | Engine | Version | Row_format | Rows | Avg_row_length | Data_length | Max_data_length | Index_length | Data_free | Auto_increment | Create_time | Update_time | Check_time | Collation | Checksum | Create_options | Comment |
+----------------------------------+--------+---------+------------+----------+----------------+-------------+-----------------+--------------+------------+----------------+---------------------+---------------------+------------+-----------------+----------+----------------+---------+
| ip_per_nat_vlan | InnoDB | 10 | Dynamic | 141291 | 100 | 14172160 | 0 | 6832128 | 25165824 | 143563 | 2017-12-24 16:26:40 | 2018-06-13 09:01:33 | NULL | utf8_unicode_ci | NULL |
MySQL says, that there should be 14172160 rows, but I dont see any. Where could be a problem? Transactions? But I dont see any running thread and no any fault.
Thank you. D
Structure of table is:
+------------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+------------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| ipAddress | varchar(255) | NO | UNI | NULL | |
| nat | int(11) | NO | | NULL | |
| vlan | int(11) | NO | | NULL | |
| district | varchar(255) | YES | | NULL | |
| idOblasti | int(11) | YES | | NULL | |
| type | varchar(255) | NO | | NULL | |
| macAddress | varchar(255) | NO | | NULL | |
+------------+--------------+------+-----+---------+----------------+

There are various ways to "count" rows in a table.
The normal way. Just count them.
select count(*) as table_rows from table_name ;
Accuracy: 100% accurate count at the time of the query is run.
using the information_schema tables
select table_rows
from information_schema.tables
where table_schema = 'database_name'
and table_name = 'table_name' ;
Accuracy: Only an approximation. If the table is the target of frequent inserts and deletes, the result can be way off the actual count. This can be improved by running ANALYZE TABLE more often.
Efficiency: Very good, it doesn't touch the table at all.
As count option is 100% accurate, your table doesn't contain any data.
Check your code and default commit option of MySQL.
Looks like you are inserting rows, but not committing them, check your index length.
Check more details here
https://dba.stackexchange.com/questions/151769/mysql-difference-between-using-count-and-information-schema-tables-for-coun

First thing, I am not sure how mysql run this line and produce the result
select count() from ip_per_nat_vlan
count() will return [Err] 1064.
count(*) or else a field name should be mentioned inside.

mysql Undo log record is too big

I have a strange problem with a particular database:
mysql> update person set last_name=null where first_name='john';
ERROR 1713 (HY000): Undo log record is too big.
What can be the problem?
(I've already googled quite a log)
mysql 5.7.20 installed with brew on Mac OSX 10.12.6.
show table status where name = 'person'
-> ;
+--------------------+--------+---------+------------+--------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+------------+--------------------+----------+----------------+---------+
| Name | Engine | Version | Row_format | Rows | Avg_row_length | Data_length | Max_data_length | Index_length | Data_free | Auto_increment | Create_time | Update_time | Check_time | Collation | Checksum | Create_options | Comment |
+--------------------+--------+---------+------------+--------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+------------+--------------------+----------+----------------+---------+
| person | InnoDB | 10 | Dynamic | 650918 | 4322 | 2813853696 | 0 | 1369833472 | 6291456 | NULL | 2017-09-12 14:31:20 | 2017-10-24 12:37:03 | NULL | utf8mb4_unicode_ci | NULL | | |
+--------------------+--------+---------+------------+--------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+------------+--------------------+----------+----------------+---------+
1 row in set (0.00 sec)

Clear error after removing .frm file

I have accidentally deleted a .frm file for a test table. The problem is that I can not drop this table and remove it from information_schema.
select * from information_schema.tables where table_name like 'testtesttest';
+---------------+--------------+--------------+------------+--------+---------+------------+------------+----------------+-------------+-----------------+--------------+-----------+----------------+-------------+-------------+------------+-----------------+----------+----------------+----------------------------------------------------------+
| TABLE_CATALOG | TABLE_SCHEMA | TABLE_NAME | TABLE_TYPE | ENGINE | VERSION | ROW_FORMAT | TABLE_ROWS | AVG_ROW_LENGTH | DATA_LENGTH | MAX_DATA_LENGTH | INDEX_LENGTH | DATA_FREE | AUTO_INCREMENT | CREATE_TIME | UPDATE_TIME | CHECK_TIME | TABLE_COLLATION | CHECKSUM | CREATE_OPTIONS | TABLE_COMMENT |
+---------------+--------------+--------------+------------+--------+---------+------------+------------+----------------+-------------+-----------------+--------------+-----------+----------------+-------------+-------------+------------+-----------------+----------+----------------+----------------------------------------------------------+
| def | report | testtesttest | BASE TABLE | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | Can't find file: './report/testtesttest.frm' (errno: 13) |
+---------------+--------------+--------------+------------+--------+---------+------------+------------+----------------+-------------+-----------------+--------------+-----------+----------------+-------------+-------------+------------+-----------------+----------+----------------+----------------------------------------------------------+
drop table report.testtesttest;
ERROR 1051 (42S02): Unknown table 'testtesttest'
Is there a way to tell mysql that such a table no longer exists?

Looks like that the following steps help:
touch /var/lib/mysql/report/testtesttest.{frm,ibd}
chown mysql:mysql /var/lib/mysql/report/testtesttest.frm
restart mysql
drop table report.testtesttest;

How can I Determine Date of Import from MySQL?

I uploaded a joomla website to my database some time ago. Now I would like to know what the exact date is that I uploaded the website. Is there a way to find this out in the database?

A quick way is to check the create_time or update_time when you execute this command:
show table status;
like the following example:
+--------------------+--------+---------+------------+------+----------------+-------------+------------------+--------------+-----------+----------------+---------------------+---------------------+------------+-------------------+----------+----------------+---------+
| Name | Engine | Version | Row_format | Rows | Avg_row_length | Data_length | Max_data_length | Index_length | Data_free | Auto_increment | Create_time | Update_time | Check_time | Collation | Checksum | Create_options | Comment |
+--------------------+--------+---------+------------+------+----------------+-------------+------------------+--------------+-----------+----------------+---------------------+---------------------+------------+-------------------+----------+----------------+---------+
| a_table | MyISAM | 10 | Dynamic | 2 | 60 | 120 | 281474976710655 | 1024 | 0 | NULL | 2011-09-08 18:26:38 | 2011-11-07 20:38:28 | NULL | latin1_swedish_ci | NULL | | |

I am sure there is another way to go about this but you can probably look inside the "data" folder and see the creation date of the mysql data files.