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Why does MySQL add a comment to InnoDB tables?

Tags:

mysql

innodb

When using phpMyAdmin or the MySQL GUI Tools, whenever I create an InnoDB table, it adds a comment to the table like this:

InnoDB free: 9216 kB

What does this mean? What's it used for?

like image 923
nickf Avatar asked Dec 16 '08 04:12

nickf

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1 Answers

InnoDB stores many tables per file. Inside that InnoDB data file, there can be free space:

  • When you drop a table or index, delete rows, or replace rows with smaller ones (e.g., shorter TEXT)
  • The file is grown n MB at a time (configured in my.cnf)

The comment is just telling you how much free space is in your InnoDB datafile(s). When that approaches 0, InnoDB will expand the data file.

I believe the default allocation block is 10MB, so that's probably why you have almost 10MB free.

like image 187
derobert Avatar answered Oct 30 '22 11:10

derobert
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