TYPO3’s reference index (short: refindex) is a crucial element of the TYPO3 Core. The main parts are the PHP class “ReferenceIndex” and the database table “sys_refindex”. In simple terms, the refindex acts as a registry of database relations attached to TCA-based table records.
This is a companion discussion topic for the original entry at https://typo3.org/article/typo3-v132-ready-set-ride