Improve user control over truncation of logged bind-parameter values.

This patch replaces the boolean GUC log_parameters_on_error introduced
by commit ba79cb5dc with an integer log_parameter_max_length_on_error,
adding the ability to specify how many bytes to trim each logged
parameter value to.  (The previous coding hard-wired that choice at
64 bytes.)

In addition, add a new parameter log_parameter_max_length that provides
similar control over truncation of query parameters that are logged in
response to statement-logging options, as opposed to errors.  Previous
releases always logged such parameters in full, possibly causing log
bloat.

For backwards compatibility with prior releases,
log_parameter_max_length defaults to -1 (log in full), while
log_parameter_max_length_on_error defaults to 0 (no logging).

Per discussion, log_parameter_max_length is SUSET since the DBA should
control routine logging behavior, but log_parameter_max_length_on_error
is USERSET because it also affects errcontext data sent back to the
client.

Alexey Bashtanov, editorialized a little by me

Discussion: https://postgr.es/m/b10493cc-a399-a03a-67c7-068f2791ee50@imap.cc

src/backend/utils/mb/stringinfo_mb.c

@@ -27,7 +27,7 @@
  * appendStringInfoStringQuoted
  *
  * Append up to maxlen bytes from s to str, or the whole input string if
- * maxlen <= 0, adding single quotes around it and doubling all single quotes.
+ * maxlen < 0, adding single quotes around it and doubling all single quotes.
  * Add an ellipsis if the copy is incomplete.
  */
 void
@@ -43,9 +43,9 @@ appendStringInfoStringQuoted(StringInfo str, const char *s, int maxlen)
 	Assert(str != NULL);
 
 	slen = strlen(s);
-	if (maxlen > 0 && maxlen < slen)
+	if (maxlen >= 0 && maxlen < slen)
 	{
-		int		finallen = pg_mbcliplen(s, slen, maxlen);
+		int			finallen = pg_mbcliplen(s, slen, maxlen);
 
 		copy = pnstrdup(s, finallen);
 		chunk_search_start = copy;

src/backend/utils/misc/guc.c

@@ -515,7 +515,6 @@ extern const struct config_enum_entry dynamic_shared_memory_options[];
  * GUC option variables that are exported from this module
  */
 bool		log_duration = false;
-bool		log_parameters_on_error = false;
 bool		Debug_print_plan = false;
 bool		Debug_print_parse = false;
 bool		Debug_print_rewritten = false;
@@ -544,6 +543,8 @@ int			log_min_messages = WARNING;
 int			client_min_messages = NOTICE;
 int			log_min_duration_sample = -1;
 int			log_min_duration_statement = -1;
+int			log_parameter_max_length = -1;
+int			log_parameter_max_length_on_error = 0;
 int			log_temp_files = -1;
 double		log_statement_sample_rate = 1.0;
 double		log_xact_sample_rate = 0;
@@ -1381,15 +1382,6 @@ static struct config_bool ConfigureNamesBool[] =
 		false,
 		NULL, NULL, NULL
 	},
-	{
-		{"log_parameters_on_error", PGC_SUSET, LOGGING_WHAT,
-			gettext_noop("Logs bind parameters of the logged statements where possible."),
-			NULL
-		},
-		&log_parameters_on_error,
-		false,
-		NULL, NULL, NULL
-	},
 	{
 		{"debug_print_parse", PGC_USERSET, LOGGING_WHAT,
 			gettext_noop("Logs each query's parse tree."),
@@ -2855,6 +2847,28 @@ static struct config_int ConfigureNamesInt[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"log_parameter_max_length", PGC_SUSET, LOGGING_WHAT,
+			gettext_noop("When logging statements, limit logged parameter values to first N bytes."),
+			gettext_noop("-1 to print values in full."),
+			GUC_UNIT_BYTE
+		},
+		&log_parameter_max_length,
+		-1, -1, INT_MAX / 2,
+		NULL, NULL, NULL
+	},
+
+	{
+		{"log_parameter_max_length_on_error", PGC_USERSET, LOGGING_WHAT,
+			gettext_noop("When reporting an error, limit logged parameter values to first N bytes."),
+			gettext_noop("-1 to print values in full."),
+			GUC_UNIT_BYTE
+		},
+		&log_parameter_max_length_on_error,
+		0, -1, INT_MAX / 2,
+		NULL, NULL, NULL
+	},
+
 	{
 		{"bgwriter_delay", PGC_SIGHUP, RESOURCES_BGWRITER,
 			gettext_noop("Background writer sleep time between rounds."),

src/backend/utils/misc/postgresql.conf.sample

@@ -545,8 +545,13 @@
 					#   %% = '%'
 					# e.g. '<%u%%%d> '
 #log_lock_waits = off			# log lock waits >= deadlock_timeout
+#log_parameter_max_length = -1		# when logging statements, limit logged
+					# bind-parameter values to N bytes;
+					# -1 means print in full, 0 disables
+#log_parameter_max_length_on_error = 0	# when logging an error, limit logged
+					# bind-parameter values to N bytes;
+					# -1 means print in full, 0 disables
 #log_statement = 'none'			# none, ddl, mod, all
-#log_parameters_on_error = off	# on error log statements with bind parameters
 #log_replication_commands = off
 #log_temp_files = -1			# log temporary files equal or larger
 					# than the specified size in kilobytes;