From: Daniele Varrazzo <daniele.varrazzo@gmail.com>
Date: Sat, 10 May 2025 02:55:45 +0000 (+0200)
Subject: docs: add section about connection logging
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=refs%2Fpull%2F1085%2Fhead;p=thirdparty%2Fpsycopg.git

docs: add section about connection logging
---

diff --git a/docs/basic/usage.rst b/docs/basic/usage.rst
index a3bb13e7b..dd0fd8f04 100644
--- a/docs/basic/usage.rst
+++ b/docs/basic/usage.rst
@@ -236,3 +236,55 @@ integration between your Python program and your PostgreSQL database:
 - If you want to customise how Python values and PostgreSQL types are mapped
   into each other, beside the :ref:`basic type mapping <types-adaptation>`,
   you can :ref:`configure your types <adaptation>`.
+
+
+.. _logging:
+
+Connection logging
+------------------
+
+Psycopg uses the `logging` module to report the operations happening at
+connection time. If you experience slowness or random failures on connection
+you can set the ``psycopg`` logger at ``DEBUG`` level to read the operations
+performed.
+
+A very simple example of logging configuration may be the following:
+
+.. code:: python
+
+    import logging
+    import psycopg
+
+    logger = logging.getLogger()
+    logging.basicConfig(level=logging.DEBUG, format="%(asctime)s %(levelname)s %(message)s")
+
+    logging.getLogger("psycopg").setLevel(logging.DEBUG)
+
+    psycopg.connect("host=192.0.2.1,localhost connect_timeout=10")
+
+In this example Psycopg will first try to connect to a non responsive server,
+only stopping after hitting the timeout, and will move on to a working server.
+The resulting log might look like:
+
+.. code:: text
+
+    2045-05-10 11:45:54,364 DEBUG connection attempt: host: '192.0.2.1', port: None, hostaddr: '192.0.2.1'
+    2045-05-10 11:45:54,365 DEBUG connection started: <psycopg_c.pq.PGconn [STARTED] at 0x79dff6d26160>
+    2045-05-10 11:45:54,365 DEBUG connection polled: <psycopg_c.pq.PGconn [MADE] at 0x79dff6d26160>
+    2045-05-10 11:46:04,392 DEBUG connection failed: host: '192.0.2.1', port: None, hostaddr: '192.0.2.1': connection timeout expired
+    2045-05-10 11:46:04,392 DEBUG connection attempt: host: 'localhost', port: None, hostaddr: '127.0.0.1'
+    2045-05-10 11:46:04,393 DEBUG connection started: <psycopg_c.pq.PGconn [STARTED] at 0x79dff6d26160>
+    2045-05-10 11:46:04,394 DEBUG connection polled: <psycopg_c.pq.PGconn [MADE] at 0x79dff6d26160>
+    2045-05-10 11:46:04,394 DEBUG connection polled: <psycopg_c.pq.PGconn [SSL_STARTUP] at 0x79dff6d26160>
+    2045-05-10 11:46:04,411 DEBUG connection polled: <psycopg_c.pq.PGconn [SSL_STARTUP] at 0x79dff6d26160>
+    2045-05-10 11:46:04,413 DEBUG connection polled: <psycopg_c.pq.PGconn [SSL_STARTUP] at 0x79dff6d26160>
+    2045-05-10 11:46:04,423 DEBUG connection polled: <psycopg_c.pq.PGconn [MADE] at 0x79dff6d26160>
+    2045-05-10 11:46:04,424 DEBUG connection polled: <psycopg_c.pq.PGconn [AWAITING_RESPONSE] at 0x79dff6d26160>
+    2045-05-10 11:46:04,426 DEBUG connection polled: <psycopg_c.pq.PGconn [IDLE] (host=localhost database=piro) at 0x79dff6d26160>
+    2045-05-10 11:46:04,426 DEBUG connection succeeded: host: 'localhost', port: None, hostaddr: '127.0.0.1'
+
+Please note that a connection attempt might try to reach different servers:
+either explicitly because the connection string specifies `multiple hosts`__,
+or implicitly, because the DNS resolves an host name to multiple IPs.
+
+.. __: https://www.postgresql.org/docs/current/libpq-connect.html#LIBPQ-MULTIPLE-HOSTS
diff --git a/docs/news.rst b/docs/news.rst
index 385ec5b87..d79dbbd70 100644
--- a/docs/news.rst
+++ b/docs/news.rst
@@ -34,6 +34,9 @@ Psycopg 3.2.8 (unreleased)
   returns `None` (:ticket:`#1073`).
 - Fix `ConnectionInfo.port` when the port is specified as an empty string
   (:ticket:`#1078`).
+- Report all the attempts error messages in the exception raised for a
+  connection failure (:ticket:`#1069`).
+- Improve logging on connection (:ticket:`#1085`).
 - Add support for PostgreSQL 18 libpq (:ticket:`#1082`).