PLA-460 use left outer join trick to filter broken links
PLA-460 Try to use name_title index for first two letters
PLA-460 Performance improvement
Page titles can't start with lowercase letter
PLA-460 revert unwanted change
PLA-460 add ORDER BY page_title to make query deterministic
PLA-460 add small comment to query
add performance tests
remove order by
Merge pull request #1317 from Wikia/PLA-460-performance-fix

PLA-460 use left join to filter broken links