Intermittent hang in SQLConnect (ODBC, PostgreSQL 15, Windows) - Mailing list pgsql-general

Hi all,

We are encountering an intermittent issue where our Windows-based application hangs indefinitely during SQLConnect when connecting to a PostgreSQL server via ODBC.

Environment

• PostgreSQL version:  15.0.15.25315
• ODBC driver: psqlODBC 16.00.0007
• Connection type: ODBC using certificate-based authentication
• Deployment: Application and PostgreSQL server both run on the same machine (localhost)

Application Behavior

• The application maintains:
  • Some long-lived persistent connections
  • A few short-lived connections (3–4) that are opened/closed periodically
• Connection pooling is enabled (we also tested with pooling disabled and reduced timeouts—no change)

Configuration

• Connection timeout is explicitly set before calling SQLConnect
• TCP keepalive parameters are configured
• Both settings are visible in PostgreSQL ODBC trace logs

Issue Description

On a subset of systems, intermittently (roughly once a week, sometimes more frequently), the SQLConnect call:

• Hangs indefinitely
• Does not return or timeout

Observations / Troubleshooting

• Initially suspected Microsoft Defender or network filtering:
  • Added PostgreSQL data directory to exclusions → no improvement
  • No network filtering/firewall issues observed
• Adjusted connection pooling and timeout values → no impact

Call Stack During Hang

mswsock!WSPStartup
mswsock!WSPStartup
ws2_32!select
libpq!PQsocketPoll
libpq!PQsocketPoll
libpq!PQgetResult
psqlodbc35w!Ordinal94
psqlodbc35w!Ordinal94
psqlodbc35w!Ordinal94
psqlodbc35w!SQLConnectW
odbc32!SQLConnectW
odbc32!ODBCSetTryWaitValue
comsvcs!DispManGetContext
comsvcs!DispManGetContext
odbc32!SQLDriverConnectW
odbc32!SQLDriverConnectW
odbc32!SQLFreeStmt
odbc32!SQLConnectW
odbc32!SQLConnect

From the stack, it appears the hang occurs in:

• libpq!PQsocketPoll / PQgetResult, which eventually blocks in
• ws2_32!select

This suggests the thread is waiting on a socket event during connection establishment (possibly SSL/certificate handshake or server response).

Questions

• Has anyone experienced similar behavior with PostgreSQL 15 and psqlODBC on Windows?
• Are there known issues where SQLConnect can block indefinitely despite configured timeouts?
• Could this be related to libpq socket polling behavior or SSL/cert authentication edge cases?

Any insights or suggestions for further diagnostics would be greatly appreciated.

Thanks in advance.