Eager Loading for ActiveRecord Performance
summary
Explains how ActiveRecord turns an N+1 into fewer queries using includes -> 2 queries and how includes chooses between the two-query preload strategy and a slower LEFT OUTER JOIN eager_load; shows preload and eager_load APIs and when to force them. Demonstrates counter_cache cutting many queries to 1 query by storing counts (migration + backfill required) and shows Russian-doll fragment caching combined with fast_jsonapi and Bullet to eliminate DB reads for warm caches; demo with 10 posts × 1,000 comments (10,000 records) validates the approach.
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chapters (7)
- 0:00Start
- 9:33Chaining
- 11:13Relations execute queries lazily
- 16:02#preload
- 28:44on a cold cache
- 32:35the power of lazy
- 34:16THE NETFLIX TECH BLOG
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