SQL query to list size of database tables

I was recently experiencing a considerable slow access issue to my Drupal webapp which was working smoothly so far.
CPU usage was very high as well as the MySQL server process but nothing unusual in the show processlist.
After digging around trying to determine what was the root cause, I ran the following SQL query just to know what the main tables in terms of disk size usage were:

SELECT CONCAT(table_schema, '.', table_name),
       CONCAT(ROUND(table_rows / 1000000, 2), 'M')                                    rows,
       CONCAT(ROUND(data_length / ( 1024 * 1024 * 1024 ), 2), 'G')                    DATA,
       CONCAT(ROUND(index_length / ( 1024 * 1024 * 1024 ), 2), 'G')                   idx,
       CONCAT(ROUND(( data_length + index_length ) / ( 1024 * 1024 * 1024 ), 2), 'G') total_size,
       ROUND(index_length / data_length, 2)                                           idxfrac
FROM   information_schema.TABLES
ORDER  BY data_length + index_length DESC
LIMIT  10;

It shows the top10 tables in terms of disk space used:

SQL Query

Out of that table I quickly realised the cache_form table was using an unexpected high size which eventually was slowing down the access to the webapp.
Truncating that table solved the issue.

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