On Mon, 2024-06-17 at 16:40 -0500, Justin Pryzby wrote:
> > The feature will become much less useful if unique voilations keep getting 
> > logged.
> 
> Uh, to be clear, your patch is changing the *defaults*, which I found
> surprising, even after reaading the thread.  Evidently, the current
> behavior is not what you want, and you want to change it, but I'm *sure*
> that whatever default you want to use at your site/with your application
> is going to make someone else unhappy.  I surely want unique violations
> to be logged, for example.

I was afraid that setting the default non-empty would cause objections.

> > +       <para>
> > +        This setting is useful to exclude error messages from the log that 
> > are
> > +        frequent but irrelevant.
> 
> I think you should phrase the feature as ".. *allow* skipping error
> logging for messages ... that are frequent but irrelevant for a given
> site/role/DB/etc."

I have reworded that part.

> I suggest that this patch should not change the default behavior at all:
> its default should be empty.  That you, personally, would plan to
> exclude this or that error code is pretty uninteresting.  I think the
> idea of changing the default behavior will kill the patch, and even if
> you want to propose to do that, it should be a separate discussion.
> Maybe you should make it an 002 patch.

I have attached a new version that leaves the parameter empty by default.

The patch is not motivated by my personal dislike of certain error messages.
A well-written application would not need that parameter at all.
The motivation for me is based on my dealing with customers' log files,
which are often full of messages that are only distracting from serious
problems and fill up the disk.

But you are probably right that it would be hard to find a default setting
that nobody has quibbles with, and the default can always be changed with
a future patch.

Yours,
Laurenz Albe
From 8e1eeb9cbcb94d9b15eb9ee97956cc4044ff7964 Mon Sep 17 00:00:00 2001
From: Laurenz Albe <laurenz.a...@cybertec.at>
Date: Tue, 18 Jun 2024 18:39:05 +0200
Subject: [PATCH v4] Add parameter log_suppress_errcodes

The parameter contains a list of SQLSTATEs for which
FATAL and ERROR messages are not logged.  This is to
suppress messages that are of little interest to the
database administrator, but tend to clutter the log.

Author: Laurenz Albe
Discussion: https://postgr.es/m/408f399e7de1416c47bab7e260327ed5ad92838c.camel%40cybertec.at
---
 doc/src/sgml/config.sgml                      |  35 ++++++
 src/backend/utils/error/elog.c                | 119 ++++++++++++++++++
 src/backend/utils/misc/guc_tables.c           |  11 ++
 src/backend/utils/misc/postgresql.conf.sample |   3 +
 src/include/pg_config_manual.h                |  10 ++
 src/include/utils/guc.h                       |   1 +
 src/include/utils/guc_hooks.h                 |   2 +
 7 files changed, 181 insertions(+)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 698169afdb..a58b43bceb 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -6883,6 +6883,41 @@ local0.*    /var/log/postgresql
       </listitem>
      </varlistentry>
 
+     <varlistentry id="guc-log-suppress-errcodes" xreflabel="log_suppress_errcodes">
+      <term><varname>log_suppress_errcodes</varname> (<type>string</type>)
+      <indexterm>
+       <primary><varname>log_suppress_errcodes</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        Causes <literal>ERROR</literal> and <literal>FATAL</literal> messages
+        from client backend processes with certain error codes to be excluded
+        from the log.
+        The value is a comma-separated list of five-character error codes as
+        listed in <xref linkend="errcodes-appendix"/>.  An error code that
+        represents a class of errors (ends with three zeros) suppresses logging
+        of all error codes within that class.  For example, the entry
+        <literal>08000</literal> (<literal>connection_exception</literal>)
+        would suppress an error with code <literal>08P01</literal>
+        (<literal>protocol_violation</literal>).  The default setting is
+        empty, that is, all error codes get logged.
+        Only superusers and users with the appropriate <literal>SET</literal>
+        privilege can change this setting.
+       </para>
+
+       <para>
+        This setting allows you to skip error logging for messages that are
+        frequent but irrelevant.  Supressing such messages makes it easier to
+        spot relevant messages in the log and keeps log files from growing too
+        big.  For example, if you have a monitoring system that regularly
+        establishes a TCP connection to the server without sending a correct
+        startup packet, you could suppress the protocol violation errors by
+        adding the error code <literal>08P01</literal> to the list.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry id="guc-log-min-duration-statement" xreflabel="log_min_duration_statement">
       <term><varname>log_min_duration_statement</varname> (<type>integer</type>)
       <indexterm>
diff --git a/src/backend/utils/error/elog.c b/src/backend/utils/error/elog.c
index d91a85cb2d..0b2506e07a 100644
--- a/src/backend/utils/error/elog.c
+++ b/src/backend/utils/error/elog.c
@@ -111,12 +111,16 @@ int			Log_error_verbosity = PGERROR_DEFAULT;
 char	   *Log_line_prefix = NULL; /* format for extra log line info */
 int			Log_destination = LOG_DESTINATION_STDERR;
 char	   *Log_destination_string = NULL;
+char	   *log_suppress_errcodes = NULL;
 bool		syslog_sequence_numbers = true;
 bool		syslog_split_messages = true;
 
 /* Processed form of backtrace_functions GUC */
 static char *backtrace_function_list;
 
+/* Processed form form of log_suppress_errcodes (zero-terminated array) */
+static int *suppressed_errcodes;
+
 #ifdef HAVE_SYSLOG
 
 /*
@@ -863,6 +867,30 @@ errcode(int sqlerrcode)
 
 	edata->sqlerrcode = sqlerrcode;
 
+	/*
+	 * ERROR and FATAL messages with codes in log_suppress_errcodes don't get
+	 * logged.  We only want to suppress error messages from ordinary backend
+	 * processes.
+	 */
+	if ((MyBackendType == B_BACKEND ||
+		 MyBackendType == B_STANDALONE_BACKEND) &&
+		(edata->elevel == ERROR ||
+		 edata->elevel == FATAL) &&
+		suppressed_errcodes != NULL)
+	{
+		int *state;
+
+		for (state = suppressed_errcodes; *state != 0; state++)
+			/* error categories match all error codes in the category */
+			if (sqlerrcode == *state ||
+				(ERRCODE_IS_CATEGORY(*state) &&
+				 ERRCODE_TO_CATEGORY(sqlerrcode) == *state))
+			{
+				edata->output_to_server = false;
+				break;
+			}
+	}
+
 	return 0;					/* return value does not matter */
 }
 
@@ -2263,6 +2291,97 @@ assign_log_destination(const char *newval, void *extra)
 	Log_destination = *((int *) extra);
 }
 
+/*
+ * GUC check_hook for log_suppress_errcodes
+ */
+bool
+check_log_suppress_errcodes(char **newval, void **extra, GucSource source)
+{
+	/* SplitIdentifierString modifies the string */
+	char *new_copy = pstrdup(*newval);
+	int listlen;
+	int *statelist = NULL;
+	int index = 0;
+	List *states;
+	ListCell *c;
+
+	if (!SplitIdentifierString(new_copy, ',', &states))
+	{
+		GUC_check_errdetail("List syntax is invalid.");
+		goto failed;
+	}
+
+	listlen = list_length(states);
+	statelist = guc_malloc(ERROR, sizeof(int) * (listlen + 1));
+
+	/* check all error codes for validity and compile them into statelist */
+	foreach(c, states)
+	{
+		char *state = lfirst(c);
+		char *p;
+		int errcode;
+
+		if (strlen(state) != 5)
+		{
+			GUC_check_errdetail("error codes must have 5 characters.");
+			goto failed;
+		}
+
+		/*
+		 * Check the the values are alphanumeric and convert them to upper case
+		 * (SplitIdentifierString converted them to lower case).
+		 */
+		for (p = state; *p != '\0'; p++)
+			if (*p >= 'a' && *p <= 'z')
+				*p += 'A' - 'a';
+			else if (*p < '0' || *p > '9')
+			{
+				GUC_check_errdetail("error codes can only contain digits and ASCII letters.");
+				goto failed;
+			}
+
+		errcode = MAKE_SQLSTATE(state[0], state[1], state[2], state[3], state[4]);
+		/* ignore 0: it cannot be an error code, and we use it to end the list */
+		if (errcode == ERRCODE_SUCCESSFUL_COMPLETION)
+			continue;
+
+		statelist[index++] = errcode;
+	}
+	statelist[index] = 0;
+
+	list_free(states);
+	pfree(new_copy);
+
+	*extra = statelist;
+	return true;
+
+failed:
+	list_free(states);
+	pfree(new_copy);
+	guc_free(statelist);
+	return false;
+}
+
+/*
+ * GUC assign_hook for log_suppress_errcodes
+ */
+void
+assign_log_suppress_errcodes(const char *newval, void *extra)
+{
+	/* free the memory for the old entries */
+	if (suppressed_errcodes != NULL)
+		pfree(suppressed_errcodes);
+
+	/* store NULL instead of an empty array for performance */
+	if (*(int *)extra == 0)
+	{
+		guc_free(extra);
+		suppressed_errcodes = NULL;
+	}
+	else
+		suppressed_errcodes = extra;
+}
+
 /*
  * GUC assign_hook for syslog_ident
  */
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index 46c258be28..0341c805b9 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -4487,6 +4487,17 @@ struct config_string ConfigureNamesString[] =
 		check_canonical_path, NULL, NULL
 	},
 
+	{
+		{"log_suppress_errcodes", PGC_SUSET, LOGGING_WHEN,
+			gettext_noop("ERROR and FATAL messages with these error codes don't get logged."),
+			NULL,
+			GUC_LIST_INPUT
+		},
+		&log_suppress_errcodes,
+		DEFAULT_LOG_SUPPRESS_ERRCODES,
+		check_log_suppress_errcodes, assign_log_suppress_errcodes, NULL
+	},
+
 	{
 		{"ssl_library", PGC_INTERNAL, PRESET_OPTIONS,
 			gettext_noop("Shows the name of the SSL library."),
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index e0567de219..eefeeff487 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -539,6 +539,9 @@
 					#   fatal
 					#   panic (effectively off)
 
+#log_suppress_errcodes = ''	# FATAL and ERROR messages with these error codes
+					# are not logged
+
 #log_min_duration_statement = -1	# -1 is disabled, 0 logs all statements
 					# and their durations, > 0 logs only
 					# statements running at least this number
diff --git a/src/include/pg_config_manual.h b/src/include/pg_config_manual.h
index f941ee2faf..8c71bc2833 100644
--- a/src/include/pg_config_manual.h
+++ b/src/include/pg_config_manual.h
@@ -216,6 +216,16 @@
  */
 #define DEFAULT_EVENT_SOURCE  "PostgreSQL"
 
+/*
+ * Default value for log_suppress_errcodes.  ERROR or FATAL messages with
+ * these error codes are never logged.  Error classes (error codes ending with
+ * three zeros) match all error codes in the class.   The idea is to suppress
+ * messages that usually don't indicate a serious problem but tend to pollute
+ * the log file.
+ */
+
+#define DEFAULT_LOG_SUPPRESS_ERRCODES ""
+
 /*
  * Assumed cache line size.  This doesn't affect correctness, but can be used
  * for low-level optimizations.  This is mostly used to pad various data
diff --git a/src/include/utils/guc.h b/src/include/utils/guc.h
index e4a594b5e8..d3ac962fa7 100644
--- a/src/include/utils/guc.h
+++ b/src/include/utils/guc.h
@@ -259,6 +259,7 @@ extern PGDLLIMPORT bool log_duration;
 extern PGDLLIMPORT int log_parameter_max_length;
 extern PGDLLIMPORT int log_parameter_max_length_on_error;
 extern PGDLLIMPORT int log_min_error_statement;
+extern PGDLLIMPORT char *log_suppress_errcodes;
 extern PGDLLIMPORT int log_min_messages;
 extern PGDLLIMPORT int client_min_messages;
 extern PGDLLIMPORT int log_min_duration_sample;
diff --git a/src/include/utils/guc_hooks.h b/src/include/utils/guc_hooks.h
index d64dc5fcdb..3b312e78fb 100644
--- a/src/include/utils/guc_hooks.h
+++ b/src/include/utils/guc_hooks.h
@@ -78,6 +78,8 @@ extern bool check_log_destination(char **newval, void **extra,
 extern void assign_log_destination(const char *newval, void *extra);
 extern const char *show_log_file_mode(void);
 extern bool check_log_stats(bool *newval, void **extra, GucSource source);
+extern bool check_log_suppress_errcodes(char **newval, void **extra, GucSource source);
+extern void assign_log_suppress_errcodes(const char *newval, void *extra);
 extern bool check_log_timezone(char **newval, void **extra, GucSource source);
 extern void assign_log_timezone(const char *newval, void *extra);
 extern const char *show_log_timezone(void);
-- 
2.45.1

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