Hi hackers, This is my first time submitting a patch to PostgreSQL, so please bear with me if I've missed anything in the process. We've been running into an issue with "target_session_attrs" when using dns-based service discovery. Currently, when libpq connects to a host with multiple A-records and the connection succeeds but is rejected due to target_session_attrs mismatch (e.g., connecting to a read-only server with target_session_attrs=read-write), it skips all remaining addresses for that hostname and moves directly to the next host in the connection string.
Looking at git history, I found this was a deliberate choice by Robert Haas in commit 721f7bd3cbc (2016), where he noted "I changed Mithun's patch to skip all remaining IPs for a host if we reject a connection based on this new parameter." The original mailing list discussion is at [1], though I wasn't able to find a clear explanation of why this approach was preferred over trying all addresses. This makes it impractical to use a single multi-A-record DNS name pointing to all cluster members with target_session_attrs=read-write to find the primary - only the first responding IP is tried before giving up on that hostname. The attached patch changes the behavior to try all addresses for a hostname before moving to the next host, matching the existing behavior for connection failures. This would enable simpler DNS-based service discovery without requiring external tools like Consul or explicit multi-host connection strings. If there was a specific reason for the original design that I'm missing, I'd be happy to learn more. Happy to address any feedback or rework the patch as needed. [1] http://postgr.es/m/CAD__OuhqPRGpcsfwPHz_PDqAGkoqS1UvnUnOnAB-LBWBW=w...@mail.gmail.com Thanks, Evgeny
0001-libpq-try-all-addresses-before-moving-to-next-host-o.patch
Description: 0001-libpq-try-all-addresses-before-moving-to-next-host-o.patch
