Identify any extensions that are modifying the Table Control Array (TCA) in ext_tables.php. Changes made to the TCA in ext_tables.php can result in performance drawbacks.

Since TYPO3 CMS 6.2 changes to $GLOBALS['TCA'] must be stored inside a folder called Configuration/TCA/Overrides with one file per modified table.
These files are named along the pattern <tablename>.php.

Thus if you want to customize the TCA of tx_foo_domain_model_bar, you’d create the file Configuration/TCA/Overrides/tx_foo_domain_model_bar.php.

The advantage of this method is that all such changes are incorporated into $GLOBALS['TCA'] before it is cached. This is thus far more efficient.