mysql ibdata1 file corrupted or increased unusually
Please keep in mind that ibdata1 is the system tablespace. It is home of the InnoDB Infrastructure. Here are the following classes of information stored in ibdata1.


Table Data Pages (if innodb_file_per_table disabled)
Table Index Pages (if innodb_file_per_table disabled)
Data Dictionary (Tablespace IDs, Logical-to-Physical Mapping to Tables)
Double Write Buffer (Handles Data Redundancy to Support Crash Recovery)
Insert Buffer (Handles Updates to Secondary Indexes)
Rollback Segments (Manages Reverse Engineering of Uncommitted Transactions)
Undo Space (Containers of Information for Rollback Operations)
Click to See Pictorial Representation of the InnoDB Infrastructure


As you can see, ibdata1 has a lot of moving parts. The fastest growing section of ibdata1 would be the undo space, especially when there are a lot of read transactions and a few write transactions. 

Please read me past posts on doing InnoDB Cleanup:


Oct 29, 2010 : Howto: Clean a mysql InnoDB storage engine?
Nov 26, 2011 : ERROR 1114 (HY000) at line 6308 in file &amp; The table user_analysis is full
Mar 25, 2012 : Why does InnoDB store all databases in one file?
Jun 19, 2012 : whether a big (but not used) ibdata1 slow anything down
Jan 07, 2013 : Database space doesn&#39;t match ibdata1 size