Important: #110454 - Translation source index covers the translation lookups 

Description 

Looking up the translations of a record matches either the translation source field (l10n_source) or - for translations written without a translation source - the combination of an empty translation source and the translation origin pointer field (l18n_parent / l10n_parent). Both alternatives have to be resolvable through a single index, otherwise MySQL reduces the condition to a range over l10n_source IN (0, <uid>) - which covers every record without a translation source, usually a large part of the table - or discards the index and scans the table.

The automatically generated translation_source index therefore no longer consists of the translation source field alone, but of the translation source field, the translation origin pointer field and the language field:

KEY translation_source (l10n_source, l18n_parent, sys_language_uid)

The former single-column index remains the leftmost prefix of the new one, so queries filtering on the translation source alone continue to use it.

In addition, the language related indexes are now generated for every language-aware table, independent of whether the underlying columns were added by the automatic TCA schema generation or declared in an ext_tables.sql file. Previously a table which declared one of those columns itself silently ended up without them.

Impact 

The database analyzer reports a changed index for every language-aware table that defines ctrl['translationSource'], and an added index for tables that declared their language related columns themselves. Both are non-destructive schema changes and should be applied during the next update, either in the Admin Tools > Maintenance > Analyze Database Structure module or with typo3 database:updateschema .

Extensions which declared an equivalent index under a different name may end up with a redundant index and can drop their own definition.