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MySQL 5.7 Reference Manual
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MySQL 5.7 Reference Manual  /  ...  /  Problems from Tables Not Being Closed Properly Problems from Tables Not Being Closed Properly

Each MyISAM index file (.MYI file) has a counter in the header that can be used to check whether a table has been closed properly. If you get the following warning from CHECK TABLE or myisamchk, it means that this counter has gone out of sync:

clients are using or haven't closed the table properly

This warning doesn't necessarily mean that the table is corrupted, but you should at least check the table.

The counter works as follows:

  • The first time a table is updated in MySQL, a counter in the header of the index files is incremented.

  • The counter is not changed during further updates.

  • When the last instance of a table is closed (because a FLUSH TABLES operation was performed or because there is no room in the table cache), the counter is decremented if the table has been updated at any point.

  • When you repair the table or check the table and it is found to be okay, the counter is reset to zero.

  • To avoid problems with interaction with other processes that might check the table, the counter is not decremented on close if it was zero.

In other words, the counter can become incorrect only under these conditions:

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