When a user uses partition selection in a SELECT query to only query a particular partition of a MyISAM table, many users would expect the server to only open the data files for that particular partition. In reality, the server opens all data files for the table.
This bug is related to partition selection in SELECT statements, as defined here:
Let's say that we create the following table:
And then we execute the following to ensure that the table's data files are closed:
And then we can confirm that the table's data files are not open:
And then let's say that we execute the following query:
Most users would expect that the server would only open the data files for partition p1. In reality, it opens all of them: