MySQL innodb row count very innacurate

They say the number of rows you see in PHPMyADMIN is approximate and not very precise for innodb tables, i can tell you that depending on how the table has been used, the results can be very very inaccurate and sometimes irrelevant.

phpmyadmin wants to display a row count with the list of tables, in myisam, a value is maintained within the database saying how many rows are in the database, INNODB does not maintain such a value so it has to either respond accurately without regard to the delay and scans required or give an approximate reading, it will depend on how you ask, read on for more details.

Q: why are innodb row counts innacurate in PHPMYADMIN ?

Well, innodb would return an accurate count if it were asked formally with a

SELECT COUNT(*) FROM tablename"

But phpmyadmin can not execute such a statement with every listing of a database, because it means the database engine will have to read the whole database and scan all rows.

Q: in that case how come it works for MyISAM ?

A: MyISAM maintains a number stating how many rows are in there that is incremented and decremented with every insert and delete, so the database engine does not need to scan the whole table to give us a row count.

Q: Then where does PHPMYADMIN get those approximate numbers ?

For speed, PHP MY ADMIN would execute something similar (If not exactly)

SHOW TABLE STATUS WHERE 1;

This is when MyISAM would read it’s internal row count value, and Innodb would return an estimate because it does not maintain such a value.

You can also use the command to see a subset of the tables like this

SHOW TABLE STATUS LIKE 'wp_%';

to see status of all tables starting with ‘wp_’

Q: Why does innodb not maintain such a number

A: probably for performance reasons, to avoid the need to update such a number with every insert and every delete.

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