Thank you for responding.
I discovered this help page that seems to relate to my problem:
http://dev.mysql.com/doc/refman/5.6/en/innodb-troubleshooting-datadict.html
Unfortunately it says nothing about partitions, and when I followed the instructions I found that MySQL deleted the #sql-15fd_3477.frm and #sql-15fd_3477.par files but not the actual data files (#sql-ibXXXX.ibd). MySQL wrote various error messages when I tryed to drop the table (I omitted a few hundred lines of similar output):
2015-02-27 14:04:37 7fbf89506700 InnoDB: Error: table `my_database`.`#sql-15fd_3477#P#p47` /* Partition `p47` */ does not exist in the InnoDB internal
InnoDB: data dictionary though MySQL is trying to drop it.
InnoDB: Have you copied the .frm file of the table to the
InnoDB: MySQL database directory from another database?
InnoDB: You can look for further help from
InnoDB:
http://dev.mysql.com/doc/refman/5.6/en/innodb-troubleshooting.html
2015-02-27 14:04:37 7fbf89506700 InnoDB: Error: table `my_database`.`#sql-15fd_3477#P#p48` /* Partition `p48` */ does not exist in the InnoDB internal
InnoDB: data dictionary though MySQL is trying to drop it.
InnoDB: Have you copied the .frm file of the table to the
InnoDB: MySQL database directory from another database?
InnoDB: You can look for further help from
InnoDB:
http://dev.mysql.com/doc/refman/5.6/en/innodb-troubleshooting.html
2015-02-27 14:04:37 7fbf89506700 InnoDB: Error: table `my_database`.`#sql-15fd_3477#P#p49` /* Partition `p49` */ does not exist in the InnoDB internal
InnoDB: data dictionary though MySQL is trying to drop it.
InnoDB: Have you copied the .frm file of the table to the
InnoDB: MySQL database directory from another database?
InnoDB: You can look for further help from
InnoDB:
http://dev.mysql.com/doc/refman/5.6/en/innodb-troubleshooting.html
2015-02-27 14:08:23 11038 [ERROR] Failed to open table my_database/#sql-15fd_3477#P#p0.
2015-02-27 14:08:23 11038 [Warning] InnoDB: Cannot open table my_database/#sql-15fd_3477#P#p0 from the internal data dictionary of InnoDB though the .frm file for the table exists. See
http://dev.mysql.com/doc/refman/5.6/en/innodb-troubleshooting.html for how you can resolve the problem.
> #sql-ibXXXX.ibd are the tmp tables that will be renamed when it finishes. Delete them.
I will try this (with backups), when possible.
> Did you run out of disk space?
It does not appear so. There were no error messages to tell me why the alter table failed.
> You seem to have a lot of secondary indexes. May we see SHOW CREATE TABLE and discuss whether some of them can be DROPped, thereby helping performance of the ALTER.
Sorry, right now I just want to clear up these temporary files.