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doc: Clarify the logging collector's guarantees.

Presently, the documentation for logging_collector says that the
collector "is designed to never lose messages," which reads as a
stronger promise than we actually make.  The collector does not
fsync the log file or retry failed writes, so log messages can go
missing after an operating system crash, power loss, or a write
error.  Reword that sentence and add a note about what is not
guaranteed.

Author: Daniel Bauman <danielbaniel@gmail.com>
Reviewed-by: Fujii Masao <masao.fujii@gmail.com>
Reviewed-by: Zhenwei Shang <a934172442@gmail.com>
Reviewed-by: Robert Treat <rob@xzilla.net>
Discussion: https://postgr.es/m/CAMtj0_a86DdDKkW-ReVpQpqjndVS6GMrwXVpQY4G3-SGY7saMQ%40mail.gmail.com
Backpatch-through: 14
This commit is contained in:
Nathan Bossart
2026-08-14 15:27:16 -05:00
parent d41b3e5865
commit 247ef8481d

View File

@@ -6808,7 +6808,7 @@ local0.* /var/log/postgresql
<note>
<para>
The logging collector is designed to never lose messages. This means
The logging collector is designed to avoid dropping messages. This means
that in case of extremely high load, server processes could be
blocked while trying to send additional log messages when the
collector has fallen behind. In contrast, <application>syslog</application>
@@ -6816,6 +6816,11 @@ local0.* /var/log/postgresql
may fail to log some messages in such cases but it will not block
the rest of the system.
</para>
<para>
The logging collector does not guarantee that log messages have
reached durable storage. It can still lose messages due to a system
crash, power loss, or an error while writing the log file.
</para>
</note>
</listitem>