In T408666: GlobalUserPage causes RequestTimeoutException due to unbatched queries in onTitleIsAlwaysKnown hook, we introduced LinkAlwaysKnownLookup, which is capable of evaluating the result of Title::isAlwaysKnown in batches. Currently, lookups of file existence are implemented using RepoGroup::findFile, which looks up one file at a time. However, RepoGroup::findFiles also exists, which is likely to be more efficient.

It seems that LocalRepo::findFiles implementation attempts to use a single SQL query, but ForeignRepo::findFiles just calls findFile in a loop (so for checks of file existence on Commons, this would actually NOT result in any performance improvement it seems). However, using the exposed batched logic makes sense, as it then means that whenever ForeignRepo::findFiles starts to actually batch things, LinkAlwaysKnownLookup would benefit from it instantly.