Symptoms
Reindexing of Product flat data index gives unknown reindexing error or “Some problem with reindexing process” error message or reindexing of Product flat data index is never completed.
Attempt to reindex it via command line gives the following error message:
$ php -f shell/indexer.php -- --reindex catalog_product_flat Product Flat Data index process unknown error: exception 'PDOException' with message 'SQLSTATE[23000]: Integrity constraint violation: 1452 Cannot add or update a child row: a foreign key constraint fails (<result 2 when explaining filename '#sql-'>, CONSTRAINT ´FK_CAT_PRD_FLAT_1_ENTT_ID_CAT_PRD_ENTT_ENTT_ID´ FOREIGN KEY (´entity_id´) REFERENCES ´catalog_product_entity´ (´entity_id)' in lib/Zend/Db/Statement/Pdo.php:228
Reason
There are references to inexisting/deleted products in catalog_product_flat_% tables.
Solution
Try to truncate ´catalog_product_flat_%´ tables (catalog_product_flat_1, catalog_product_flat_2, catalog_product_flat_3 etc.) in MySQL console or via phpMyAdmin:
mysql > truncate table ´catalog_product_flat_1´; mysql > truncate table ´catalog_product_flat_2´; mysql > truncate table ´catalog_product_flat_3´;