The Performance Impact of SQL’s FILTER Clause February 6, 2023.How to Write a Derived Table in jOOQ February 24, 2023.How to use jOOQ’s Converters with UNION Operations March 2, 2023.3.18.0 Release with Support for more Diagnostics, SQL/JSON, Oracle Associative Arrays, Multi dimensional Arrays, R2DBC 1.0 March 8, 2023.How to Turn a List of Flat Elements into a Hierarchy in Java, SQL, or jOOQ March 24, 2023.How to Pass a Table Valued Parameter to a T-SQL Function with jOOQ April 25, 2023.How to Generate Package Private Code with jOOQ’s Code Generator June 28, 2023.jOOQ 3.15's New Multiset Operator Will Change How You Think About SQL.10 Easy Steps to a Complete Understanding of SQL.How SQL DISTINCT and ORDER BY are Related.How to Find the Longest Consecutive Series of Events in SQL.10 SQL Tricks That You Didn't Think Were Possible.3 Reasons why You Shouldn't Replace Your for-loops by Stream.forEach().Using SQL Injection Vulnerabilities to Dump Your Database.Faster SQL Pagination with jOOQ Using the Seek Method.Say NO to Venn Diagrams When Explaining JOINs.Join 2,144 other subscribers Top Posts & Pages The benchmark technique is described here. RAISE INFO 'Run %, Statement 2: %', r, (clock_timestamp() - v_ts) SUM(CASE WHEN rating = 'PG' THEN length END) SUM(CASE WHEN rating = 'R' THEN length END), RAISE INFO 'Run %, Statement 1: %', r, (clock_timestamp() - v_ts) Repeat the whole benchmark several times to avoid warmup penalty Benchmark codeĪs promised, this was the benchmark code used for this blog post: Do measure things yourself, and if you cannot reproduce a performance problem, then don’t necessarily touch perfectly sound logic just because a blog post told you so. While in this case, the improvement is worth it irrespective of actual measurements (because performance can hardly be worse, and readability actually improves), always be careful with such benchmark results. You can safely switch to this nice standard SQL syntax already now. ) is such a popular idiom, and 8% is quite the significant improvement, that I think PostgreSQL should fix this. I think this is a case where it’s worth looking into simple patterns of expressions in aggregate functions. In RDBMS that don’t have such a cache, optimisation time is more costly per query, so less can be expected. Db2, Oracle, SQL Server), in case of which the optimisation needs to be done only once per cached plan, and then the plan can be reused. There was a tendency of such optimisations being favoured by RDBMS that have an execution plan cache (e.g. In a previous blog post (which is probably outdated by now), I’ve shown a lot of these cases, where the optimisation decision doesn’t depend on any cost model and data sets and should always be done, ideally. But this isn’t always the case in the real world, where optimisers make tradeoffs between: In a perfect world, two provably equivalent SQL syntaxes also perform the same way. But still, the FILTER clause outperforms CASE clause usage. The optimiser doesn’t optimise this as well as it could). So, indeed, the redundant predicate improved things (in a perfect world, it shouldn’t, but here we are.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |