PostgreSQL: Index Scan vs. Seq Scan Performance on Large Join Queries with JSONB Data
I'm collaborating on a project where I'm attempting to set up Hey everyone, I'm running into an issue that's driving me crazy. I'm relatively new to this, so bear with me. I'm experiencing significant performance issues with a query that involves joining two large tables, one of which has a JSONB column. The query is supposed to filter based on a specific key within the JSONB data, but I'm noticing that PostgreSQL is opting for a sequential scan instead of using the index I've created. Here's a simplified version of my query: ```sql SELECT t1.id, t1.name, t2.data FROM table1 t1 JOIN table2 t2 ON t1.id = t2.foreign_id WHERE t2.data ->> 'key' = 'value'; ``` I've created an index on the JSONB column like this: ```sql CREATE INDEX idx_table2_data_key ON table2 USING GIN (data -> 'key'); ``` However, when I run `EXPLAIN ANALYZE` on my query, it shows that it's doing a Seq Scan on `table2`, which is not what I expected. The table has over a million rows, and this performance is unacceptable for my application. I've tried: - Running `VACUUM ANALYZE` on both tables to update statistics. - Checking if there are any conflicting settings in the PostgreSQL configuration that might affect the planner's decision. - Running the query with different `SET enable_seqscan = off;` to force index usage, and it does use the index, but it’s still not optimal in terms of performance. I suspect that the way I'm filtering the JSONB data might not be leveraging the index efficiently. Does anyone have insights on how to optimize this query or suggest alternative approaches for working with JSONB data in joins? I'm using PostgreSQL version 13.3. Any help would be greatly appreciated! This is part of a larger service I'm building. I'd really appreciate any guidance on this. I'm coming from a different tech stack and learning Sql. Any help would be greatly appreciated! For context: I'm using Sql on Windows 11. Any advice would be much appreciated. I'm working with Sql in a Docker container on Ubuntu 22.04. Any ideas how to fix this? Any examples would be super helpful.