PostgreSQL: Unexpectedly Slow Performance on DISTINCT Queries with Large Datasets
I'm working on a project and hit a roadblock. I can't seem to get I'm a bit lost with I've tried everything I can think of but Quick question that's been bugging me - I'm experiencing important performance optimization when executing DISTINCT queries on a large dataset in PostgreSQL 13. I've been working with a table that contains over 10 million records, and when I try to retrieve unique values from a specific column, the query execution time seems to increase drastically. Here's a simplified version of the query I'm using: ```sql SELECT DISTINCT column_name FROM large_table WHERE some_condition = true; ``` Despite having an index on `column_name`, the query still takes several seconds to execute. I've tried using `EXPLAIN ANALYZE` to get insights into the query execution plan, and here’s the output: ```plaintext Seq Scan on large_table (cost=0.00..1234567.89 rows=1000000 width=...) Filter: (some_condition = true) ``` It shows that a sequential scan is being performed instead of utilizing the index, which I suspect is contributing to the slowness. I've considered creating a materialized view to cache the distinct values, but I’m not sure if that would be efficient given the frequency of updates to `large_table`. I've also read about using CTEs to possibly improve performance but haven't had much luck with those either. Has anyone faced similar issues, and if so, what optimizations would you recommend for dealing with such large datasets in PostgreSQL? Any insights on how to force the index to be used or alternative approaches would be greatly appreciated! I'm developing on Debian with Sql. Could someone point me to the right documentation? Any ideas what could be causing this? This is for a CLI tool running on Debian. Hoping someone can shed some light on this. I recently upgraded to Sql LTS. Thanks for your help in advance!