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_posts/2024/2024-06-01-query-plan.md

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+---
+layout: post
+title: "Notes on query plan optimization in RDBMS"
+description: ""
+category: 
+tags: [paper, db]
+--- 
+
+* Steps in Query Processing: query -> parsing -> RA expressions -> optimizer with stats -> execution plan -> eval engine with data -> output
+* Query optimizers use equivalence rules to systematically generate expressions equivalent to the given expression, i.e., heuristic optimization and cost-based optimization
+* Frequently used approach: heuristic rewriting of nested block structure and aggregation. Followed by cost-based join-order optimization for each block
+* Optimizers often use simple heuristics for very cheap queries, and perform exhaustive enumeration for more expensive queries 
+* Push down projection also reduces number of pages since it eliminates columns early
+* Heuristics 
+ * Consider only left-deep plans
+ * Avoid Cartesian products
+ * Don’t optimize the entire query at once. Break query into query blocks and optimize one block at a time
+   * A query block contains a single SELECT-FROM-WHERE expression as well as GROUP BY, HAVING clauses
+
+
+
+### References
+
+* [Chapter 12: Query Processing](https://www.cbcb.umd.edu/confcour/Spring2014/CMSC424/Query_processing.pdf)
+* [Chapter 13: Query Optimization](https://www.cbcb.umd.edu/confcour/Spring2014/CMSC424/query_optimization.pdf)
+* [Query Optimization](https://cs186berkeley.net/fa20/resources/static/notes/n09-QueryOpt.pdf)
+* [Relational Query Optimization I: The Plan Space](https://drive.google.com/file/d/1EDL712gC8NDO1iRI3_EjtltiQOwpitmX/view)
+* [Query Optimization](https://web.wlu.ca/science/physcomp/ikotsireas/CP465/W2-QueryOptimization/Query_Optimization.pdf)
+