Certain parts of comment rendering triggered sql queries that we didn't
really need to do. Rework things to avoid this.
* Preload comment creators in order to display commenter names with link_to_user.
* Preload comment votes in order to display "undo vote" links. Only preload
votes for members since anonymous users can't vote and don't have "undo
vote" links.
* Rework various conditionals to do the filtering in Ruby so that we
avoid issuing any extra queries in sql.
* Avoid issuing any queries at all when the post doesn't have any
comments (when last_commented_at is blank).
Changes:
* Drop Users.id_to_name.
* Don't cache Users.name_to_id.
* Replace calls to name_to_id with find_by_name when possible.
* Don't autodefine creator_name in belongs_to_creator.
* Don't autodefine updater_name in belongs_to_updater.
* Instead manually define creator_name / updater_name only on models that need
to return these fields in the api.
id_to_name was cached to reduce the impact of N+1 query patterns in
certain places, especially in api responses that return creator_name /
updater_name fields. But it still meant we were doing N calls to
memcache. Using `includes` to prefetch users avoids this N+1 pattern.
name_to_id had no need be cached, it was never used in any performance-
sensitive contexts.
Avoiding caching also avoids the need to keep these caches consistent.
* Drop /posts?ro=true param (broken).
* Clean up tag_match (rescuing PG::ConnectionBad didn't do anything, we
just build the query here, we don't run it).
* Don't allow adding tags with invalid names when they already exist in
the tags table.
* If an invalid tag is added, show an warning and ignore the tag instead
of failing with a hard error.
* Move the _(cosplay) tag validation into the tag name validator.
During single-tag searches we look up the tag once in Post.fast_count
and later on when rendering the wiki excerpt. Doing a raw query here
meant that Rails couldn't cache the query, so it got ran again when
rendering the excerpt.
Post.fast_count calls Tag.normalize_query to normalize the tag string
used for the pfc cache key. This slightly improves cache sharing at the
expense of an extra query during tag searches. The extra query isn't
worth it.
Refactor various post_tag_match methods to use subqueries instead of joins.
This simplifies things inside PostQueryBuilder, since now we can assume
we're always dealing with a Post relation, rather than some other table
joined with the posts table.
Move Post#humanized_essential_tag_string to TagSetPresenter#humanized_essential_tag_string.
This allows humanized_essential_tag_string to reuse the same set of tags
already fetched by the tag set presenter for the sidebar.
This avoids fetching the tag categories from memcache again (via
Post#typed_tags) when we're already fetched the tags once before.
This also means it's no longer necessary to cache humanized_essential_tag_string
itself in memcache, since it can be generated as quickly as the sidebar taglist.
Fixes the 'Approve' link in the modqueue and in the quickmod bar being
shown as available on the approver's own flagged uploads, even though
they can't actually approve these posts.
