In today's 5mins of #Postgres, we talk about an improvement to the Postgres query planner in the upcoming Postgres 17, when it comes to materialized CTEs, and column statistics as well as sort order available to the upper plan level. Materialized CTEs are actually less likely today - if you recall Postgres 12 changed the default so a simple CTE like "WITH cte_table AS ( ... ) SELECT ... FROM cte_table" will typically pull up the query inside the "cte_table" to the top level, as if it was written as a sub-SELECT. But if you either use the MATERIALIZED keyword explicitly (because you want the planner to treat it as an optimization fence), or if Postgres can't find a way to pull up the CTE, you will see an explicit "CTE Scan" in your query plan. If you do, you might be surprised about the limited information that Postgres previously provided to plan nodes consuming that CTE Scan. Specifically, only row counts and width, but no other information like column statistics or previous sort orders were passed along. This is fixed in Postgres 17 thanks to the work of Jian Guo, Tom Lane and Richard Guo. Watch the full episode, or read the transcript for all the details, including example query plans that will change: https://lnkd.in/dsAJ7mMq
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Are you using IN lists or ANY= in your queries with #Postgres? The answer is probably yes. And with the recently committed change to Postgres 17, you will likely see noticeable performance improvements for such queries. In today's 5mins of Postgres, we take a look at the recent B-Tree Index Scan improvements committed by Peter Geoghegan, co-authored by Matthias van de Meent. This improves how ScalarArrayOpExpr (e.g. an IN list) are treated by the B-Tree index scan logic in Postgres, avoiding duplicate leaf page access, and producing better query plans when using multiple IN clauses on different columns. Watch the full episode for all the details:
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