Hello,
I would like to report a scalability issue I observed during logical replication initialization.
The problem is not that replication fails or behaves incorrectly. However, initialization time appears to increase significantly as the number of tables in a publication grows.
While investigating, I noticed the following query being executed:
SELECT DISTINCT (CASE WHEN (array_length(gpt.attrs, 1) = c.relnatts) THEN NULL ELSE gpt.attrs END)
FROM pg_publication p, LATERAL pg_get_publication_tables(p.pubname) gpt, pg_class c
WHERE gpt.relid = 236073 AND c.oid = gpt.relid AND p.pubname IN ('p1');
According to AWS Performance Insights, this query shows an average latency of more than 130 ms and approximately 113,799 buffer hits per execution when the publication contains around 10,000 tables.
As a result, the subscription initialization rate degrades from roughly 28 tables/second with 500 tables in the publication to about 8 tables/second with 10,000 tables.
In my environment, replication itself works correctly, but initialization time increases substantially as publication size grows. Unfortunately, some of my deployments contain very large schemas, with over 1 million tables on the publisher side, making this behavior a practical problem.
I can provide PostgreSQL version information, execution plans, and reproduction details if needed.
Thank you for your time.
Best regards,
Sergii
