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Deferred Join: A Deep Dive

hackmysql.com · 4,077 words · saved by 1 readers

With a simple SQL rewrite, deferred join can make a query 2x faster or more. It’s true! Now that I have your attention… “Misunderstood” is too strong because I think the people who’ve written about it understand it correctly. It would be more accurate to say “Deferred join is not explained well or thoroughly”, but that’s too wordy—it doesn’t catch your attention like the pithy parallelism in the lead. You might reap the benefits of a deferred join with a poor explanation. But let me provide you a “rich” explanation of deferred join so that you can truly deepen your understanding of, and skill with, MySQL query optimization. After all, it’s not every day we get to examine the magic of an advanced yet simple query optimization. In April 2007, Peter Zaitsev first blogged about this query optimization by another name: Using delayed JOIN to optimize count(*) and LIMIT queries. But don’t bother reading that 16 year old blog post because he doesn’t explain why the join is “delayed”, and he do

◯ Deferred Join: A Deep Dive Aug 9, 2023 #mysql #deferred-join #query-optimizaiton #finch Deferred join is powerful. Deferred join is simple. Deferred join is misunderstood. With a simple SQL rewrite, deferred join can make a query 2x faster or more. It's true! Now that I have your attention… "Misunderstood" is too strong because I think the people who've written about it understand it correctly. It would be more accurate to say "Deferred join is not explained well or thoroughly", but that's too wordy—it doesn't catch your attention like the pithy parallelism in the lead. You might reap t

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