PostgreSQL 14 - implementing Recursive CTE and Performance on Large Datasets
I've been struggling with this for a few days now and could really use some help... I'm working with performance optimization when using a recursive Common Table Expression (CTE) in PostgreSQL 14 with a large dataset. The CTE is designed to traverse a hierarchy stored in a table, but as the data grows, the execution time increases significantly, and sometimes it even times out. Here’s the recursive CTE I’m using: ```sql WITH RECURSIVE org_chart AS ( SELECT id, name, manager_id FROM employees WHERE manager_id IS NULL UNION ALL SELECT e.id, e.name, e.manager_id FROM employees e INNER JOIN org_chart oc ON e.manager_id = oc.id ) SELECT * FROM org_chart; ``` I've indexed the `manager_id` column, but it doesn't seem to help with the recursion performance. After running EXPLAIN ANALYZE, I noticed that it’s doing a lot of sequential scans, which is leading to high execution times. Here’s part of the EXPLAIN output: ``` Seq Scan on employees (cost=0.00..12345.67 rows=123456 width=64) ``` I’ve tried adjusting the `work_mem` setting in the PostgreSQL configuration to allow for more memory during sort operations, but it hasn't made a noticeable difference. I’m also considering whether restructuring the CTE or breaking down the query into smaller pieces could improve the performance. Has anyone faced similar issues and found effective strategies to optimize recursive CTEs in PostgreSQL? Any suggestions on best practices for handling large hierarchical queries would be greatly appreciated. I'm working on a CLI tool that needs to handle this. The stack includes Sql and several other technologies. How would you solve this?