Performance issues with path alias generated queries on PostgreSQL

Problem/Motivation

Queries generated by AliasStorage::preloadPathAlias() taking huge amount of time to execute. A good example is the /admin/content page which takes 10 seconds and more to load for around 75k nodes.

SQL-Query example below:

2018-07-24 11:02:11 NZST [4923-1] drupal-site@drupal-site LOG:  duration: 10990.918 ms  statement: SELECT url_alias.source AS source, url_alias.alias AS alias, langcode AS langcode, pid AS pid
        FROM 
        url_alias url_alias
        WHERE ((source::text ILIKE '/node/28') OR (source::text ILIKE '/node/29') OR (source::text ILIKE '/node/30') OR (source::text ILIKE '/node/31') OR (source::text ILIKE '/node/24') OR (source::text ILIKE '/node/25') OR (source::text ILIKE '/node/26') OR (source::text ILIKE '/node/27') OR (source::text ILIKE '/node/23') OR (source::text ILIKE '/node/211996') OR (source::text ILIKE '/user/13') OR (source::text ILIKE '/node/87382') OR (source::text ILIKE '/node/134983') OR (source::text ILIKE '/user/25222') OR (source::text ILIKE '/node/216888') OR (source::text ILIKE '/node/149705') OR (source::text ILIKE '/node/216524') OR (source::text ILIKE '/node/209767') OR (source::text ILIKE '/user/24341') OR (source::text ILIKE '/node/216536') OR (source::text ILIKE '/node/135065') OR (source::text ILIKE '/user/53277') OR (source::text ILIKE '/node/173142') OR (source::text ILIKE '/user/30085') OR (source::text ILIKE '/node/188349') OR (source::text ILIKE '/user/69670') OR (source::text ILIKE '/node/147160') OR (source::text ILIKE '/node/147245') OR (source::text ILIKE '/node/174863') OR (source::text ILIKE '/user/59491') OR (source::text ILIKE '/node/216527') OR (source::text ILIKE '/node/174530') OR (source::text ILIKE '/node/178984') OR (source::text ILIKE '/node/154121') OR (source::text ILIKE '/node/172192') OR (source::text ILIKE '/node/216869') OR (source::text ILIKE '/user/93926') OR (source::text ILIKE '/node/216876') OR (source::text ILIKE '/node/216881') OR (source::text ILIKE '/user/93929') OR (source::text ILIKE '/node/215571') OR (source::text ILIKE '/user/58627') OR (source::text ILIKE '/taxonomy/term/50463') OR (source::text ILIKE '/node/202776') OR (source::text ILIKE '/user/47599') OR (source::text ILIKE '/node/210401') OR (source::text ILIKE '/node/215338') OR (source::text ILIKE '/node/87208') OR (source::text ILIKE '/node/190312') OR (source::text ILIKE '/node') OR (source::text ILIKE '/user/1')) AND (langcode IN ('en', 'und'))
        ORDER BY langcode ASC NULLS FIRST, pid ASC NULLS FIRST

Not sure what part of Drupal this issue is actually coming from path alias or PostgreSQL driver.

Proposed resolution

1. Lower all existing aliases in url_aliases so that no ILIKE condition is required any more.
2. Make sure all new aliases are stored lowercase.

Remaining tasks

Finalize patch

User interface changes

None

API changes

Data model changes