Optimizing database access
Drupal's flexibility tends to add a lot of redundant queries, which can greatly affect the performance of your instance, especially if your instance is heavily used.
You can especially run into this type of query, run at each page call :
SELECT t.word AS realword, i.word FROM search_total t LEFT JOIN search_index i ON t.word = i.word WHERE i.word IS NULL;
Which you can easily solve this by adding the following index to your database (Postgres here, which is recommanded) :
CREATE INDEX IF NOT EXISTS locales_source_source_context_textgroup_idx ON locales_source (source, context, textgroup);