resolution_family: extend to DNS cache bypass path and PgSQL

[renecannao]

Context

PR #5554 adds mysql-resolution_family to control IPv4/IPv6 resolution in the DNS cache resolver thread. However, there are two gaps:

1. DNS cache bypass path

When the DNS cache does not contain an entry (cache miss), mysql_connection.cpp:connect_start_DNS_lookup() passes the raw hostname to mysql_real_connect, which resolves it via the MariaDB client library (pvio_socket.c) using hardcoded AF_UNSPEC. The resolution_family setting has no effect in this path.

Fixing this requires either:

• Patching the MariaDB client library to accept an ai_family hint
• Pre-resolving the hostname in ProxySQL before calling mysql_real_connect (even on cache miss)

2. PgSQL equivalent

pgsql-resolution_family should be added with the same semantics, covering the PgSQL DNS resolver thread and connection paths.

Related code paths using hardcoded AF_UNSPEC

• lib/mysql_connection.cpp:962 — DNS cache miss fallback (via MariaDB client lib)
• lib/GTID_Server_Data.cpp:160 — GTID server connections
• lib/ProxySQL_Statistics.cpp:1913 — statistics connections

References

• PR Add mysql-resolution_family to control IPv4/IPv6 hostname resolution #5554 — initial mysql-resolution_family implementation

[coderabbitai]

🔗 Related PRs

#5344 - Fix wrong index in connection cleanup loops (MySQL and PgSQL) [merged]
#5360 - fix: crash on macOS/FreeBSD when running PostgreSQL queries [merged]
#5361 - Add protocol labels for all PostgreSQL metrics and extend prometheus metrics coverage [merged]
#5421 - Harden PostgreSQL connection handling against unstable backends and error scenarios - P1 [merged]
#5443 - Add protocol label to connpool Prometheus metrics [merged]

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