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PERF: work around LIMIT breaking query plan 

(CTE is a optimisation boundary, so limit no longer has any effect on plan)
This commit is contained in:
Sam 2014-09-10 22:19:24 +10:00
parent c80ef9e3fa
commit ca2100d012
1 changed files with 3 additions and 1 deletions
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4
app/models/topic_tracking_state.rb
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@ -130,6 +130,7 @@ class TopicTrackingState
new = TopicQuery.new_filter(Topic, "xxx").where_values.join(" AND ").gsub!("'xxx'", treat_as_new_topic_clause) new = TopicQuery.new_filter(Topic, "xxx").where_values.join(" AND ").gsub!("'xxx'", treat_as_new_topic_clause)
sql = <<SQL sql = <<SQL
WITH x AS (
SELECT u.id AS user_id, SELECT u.id AS user_id,
topics.id AS topic_id, topics.id AS topic_id,
topics.created_at, topics.created_at,
@ -163,7 +164,8 @@ SQL
if topic_id if topic_id
sql << " AND topics.id = :topic_id" sql << " AND topics.id = :topic_id"
end end
sql << " ORDER BY topics.bumped_at DESC LIMIT 500"
sql << " ORDER BY topics.bumped_at DESC ) SELECT * FROM x LIMIT 500"
SqlBuilder.new(sql) SqlBuilder.new(sql)
.map_exec(TopicTrackingState, user_ids: user_ids, topic_id: topic_id) .map_exec(TopicTrackingState, user_ids: user_ids, topic_id: topic_id)