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POLost automatic ActiveRecord caching by migrating from Rails 3 to Rails 4
 

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  1. POLost automatic ActiveRecord caching by migrating from Rails 3 to Rails 4
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    <p>I have a rather intense method processing rather large batches of things. It depends on ActiveRecord to be conservative about hitting database with exact same query zillion of times.</p> <p>This is what I had in Rails 3:</p> <pre><code> CACHE (0.0ms) SELECT `song_work_numbers`.* FROM `song_work_numbers` ... CACHE (0.0ms) SELECT `variance_statement_line_matches`.* FROM `variance_statement_line_matches` ... CACHE (0.0ms) SELECT `songs`.* FROM `songs` ... CACHE (0.0ms) SELECT `variance_statement_line_matches`.* ... CACHE (0.0ms) SELECT COUNT(*) FROM `productions` ... CACHE (0.0ms) SELECT `productions`.* FROM `productions` ... ProductionWorkNumber Load (0.6ms) SELECT `production_work_numbers`.* FROM `production_work_numbers` ... SQL (0.4ms) SELECT COUNT(*) FROM `production_episodes` ... ProductionEpisode Load (0.4ms) SELECT `production_episodes`.* FROM `production_episodes` ... Processed Line [449] in 0.010037 s CACHE (0.0ms) SELECT `song_work_numbers`.* FROM `song_work_numbers` ... CACHE (0.0ms) SELECT `variance_statement_line_matches`.* FROM `variance_statement_line_matches` ... CACHE (0.0ms) SELECT `songs`.* FROM `songs` ... CACHE (0.0ms) SELECT `production_work_numbers`.* FROM `production_work_numbers` ... CACHE (0.0ms) SELECT `variance_statement_line_matches`.* FROM `variance_statement_line_matches` ... CACHE (0.0ms) SELECT COUNT(*) FROM `productions` ... CACHE (0.0ms) SELECT `productions`.* FROM `productions` ... CACHE (0.0ms) SELECT `production_work_numbers`.* FROM `production_work_numbers` ... CACHE (0.0ms) SELECT COUNT(*) FROM `production_episodes` ... CACHE (0.0ms) SELECT `production_episodes`.* FROM `production_episodes` ... Processed Line [450] in 0.006033 s </code></pre> <p>And this is what I get in Rails 4</p> <pre><code> SongWorkNumber Load (1.5ms) SELECT `song_work_numbers`.* FROM `song_work_numbers` ... Variance::StatementLineMatch Load (0.4ms) SELECT `variance_statement_line_matches`.* FROM `variance_statement_line_matches` ... Song Load (0.5ms) SELECT `songs`.* FROM `songs` ... ProductionWorkNumber Load (1.9ms) SELECT `production_work_numbers`.* FROM `production_work_numbers` ... Variance::StatementLineMatch Load (0.9ms) SELECT `variance_statement_line_matches`.* FROM `variance_statement_line_matches` ... (2.9ms) SELECT COUNT(*) FROM `productions` ... Production Load (1.5ms) SELECT `productions`.* FROM `productions` ... ProductionWorkNumber Load (1.7ms) SELECT `production_work_numbers`.* FROM `production_work_numbers` ... (0.6ms) SELECT COUNT(*) FROM `production_episodes` ... ProductionEpisode Load (112.2ms) SELECT `production_episodes`.* FROM `production_episodes` ... [Processed line 449 in 0.137435 sec] SongWorkNumber Load (1.5ms) SELECT `song_work_numbers`.* FROM `song_work_numbers` ... Variance::StatementLineMatch Load (0.4ms) SELECT `variance_statement_line_matches`.* FROM `variance_statement_line_matches` ... Song Load (0.5ms) SELECT `songs`.* FROM `songs` ... ProductionWorkNumber Load (1.7ms) SELECT `production_work_numbers`.* FROM `production_work_numbers` ... Variance::StatementLineMatch Load (0.4ms) SELECT `variance_statement_line_matches`.* FROM `variance_statement_line_matches` ... (0.5ms) SELECT COUNT(*) FROM `productions` ... Production Load (1.5ms) SELECT `productions`.* FROM `productions` ... ProductionWorkNumber Load (1.9ms) SELECT `production_work_numbers`.* FROM `production_work_numbers` ... (0.6ms) SELECT COUNT(*) FROM `production_episodes` WHERE ... ProductionEpisode Load (0.5ms) SELECT `production_episodes`.* FROM `production_episodes` ... [Processed line 450 in 0.023306 sec] </code></pre> <p>As you can see this is much much slower. When going over 50K+ lines those milliseconds really add up.</p> <p>Queries are identical. Code is the same. The only difference is that in Rails 4 version that code is ran from the delayed_job and in Rails 3 it was handled during normal browser request.</p> <p>Is there a setting or something that I missed?</p>
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    1. COYup, delayed_job is indeed different than a request coming from rack. Have you tried using delayed_job in Rails 3 and comparing the results?
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    2. COYes, it does seem like ActiveRecord::ConnectionAdapters::QueryCache is not being used in delayed_job for some reason. Still digging around to find out why. I want to use background processing anyways, but I guess it's not directly related to Rails 4.
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    3. COOut of curiosity does Rails 3 version cache all your subsequent query when running in background and also can you show you code
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