PERF: Use different column for better query plan #14748
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Using topics.id provides a better query plan than posts.topic_id which speeds up search by almost 50%.
pmusaraj
approved these changes
Oct 27, 2021
tgxworld
reviewed
Oct 27, 2021
| @@ -86,8 +86,8 @@ class Post < ActiveRecord::Base | |||
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| scope :private_posts_for_user, ->(user) do | |||
| where( | |||
| "posts.topic_id IN (#{Topic::PRIVATE_MESSAGES_SQL_USER}) | |||
| OR posts.topic_id IN (#{Topic::PRIVATE_MESSAGES_SQL_GROUP})", | |||
| "topics.id IN (#{Topic::PRIVATE_MESSAGES_SQL_USER}) | |||
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This feels a little off because this change assumes that we’ve already joined on the topics table before applying the scope. If I call Post.private_posts_for_user, I think this will blow up?
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Yes, it will. At this moment is only used in search.rb anyway, where that is already the case. I think I can add a joins(:topic) to fix that.
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Hmm maybe we should leave a comment here so that people know this is currently used for search only and that is why we join on the topics table instead of just using the topic_id column
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Using topics.id provides a better query plan than posts.topic_id which
speeds up search by almost 50%.