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Benchmark.measure


1. no join query but 3 times sql call
puts Benchmark.measure { 
	article_ids = Article.onwer_index_all(user_id).collect(&:id)
	tag_ids = Gutentag::Tagging.where("taggable_type = 'Article'").where(taggable_id: article_ids).collect(&:tag_id)
	tags = Gutentag::Tag.where(id: tag_ids).order("taggings_count DESC")
}
0.005433   0.000419   0.005852 (  0.015028)

2. left join
puts Benchmark.measure { 
	tags = Gutentag::Tag.joins("INNER JOIN gutentag_taggings ON gutentag_tags.id = gutentag_taggings.taggable_id INNER JOIN articles ON gutentag_taggings.taggable_id = articles.id AND gutentag_taggings.taggable_type = 'Article'").where(articles: {user_id: user_id}).all.distinct("gutentag_tags.name")
}
0.000511   0.000004   0.000515 (  0.000514)


no join query is 0.015028
left join elapse time is 0.000514

left join is 29 times as fast as 3 times sql call

#bench (1) #rails (38)
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