On Wed, 18 Jan 2017 13:26:46 +0900
Michael Paquier <michael.paqu...@gmail.com> wrote:

> On Wed, Jan 18, 2017 at 11:36 AM, Karl O. Pinc <k...@meme.com> wrote:
> > On Wed, 18 Jan 2017 11:08:25 +0900
> > Michael Paquier <michael.paqu...@gmail.com> wrote:
> >  
> >> Our ideas rather map here, ERRCODE_INTERNAL_ERROR would be adapted
> >> for this situation. Do any of you want to give it a shot or should
> >> I?  

> What do you think about that?
> +       log_filepath = strchr(lbuffer, ' ');
> +       if (log_filepath == NULL)
> +       {
> +           /*
> +            * Corrupted data found, return NULL to the caller and
> still
> +            * inform him on the situation.
> +            */
> +           ereport(WARNING,
> +                   (ERRCODE_INTERNAL_ERROR,
> +                    errmsg("corrupted data found in \"%s\"",
> +                           LOG_METAINFO_DATAFILE)));
> +           break;
> +       }

You must write

  errcode(ERRCODE_INTERNAL_ERROR)

instead of just
  
  ERRCODE_INTERNAL_ERROR

If you don't you get back 01000 for the error code.
Test by using psql with '\set VERBOSITY verbose'.

v26 patch attached which fixes this.

Regards,

Karl <k...@meme.com>
Free Software:  "You don't pay back, you pay forward."
                 -- Robert A. Heinlein
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 07afa3c..3188496 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4248,6 +4248,25 @@ SELECT * FROM parent WHERE key = 2400;
         <xref linkend="guc-logging-collector"> must be enabled to generate
         CSV-format log output.
        </para>
+       <para>
+        When either <systemitem>stderr</systemitem> or
+        <systemitem>csvlog</systemitem> are included, the file
+        <filename>current_logfiles</> gets created and records the location
+        of the log file(s) currently in use by the logging collector and the
+        associated logging destination. This provides a convenient way to
+        find the logs currently in use by the instance. Here is an example of
+        contents of this file:
+<programlisting>
+stderr pg_log/postgresql.log
+csvlog pg_log/postgresql.csv
+</programlisting>
+        Note that this file gets updated when a new log file is created
+        as an effect of rotation or when <varname>log_destination</> is
+        reloaded.  <filename>current_logfiles</> is removed when
+        <systemitem>stderr</systemitem> and <systemitem>csvlog</systemitem>
+        are not included in <varname>log_destination</> or when the
+        logging collector is disabled.
+       </para>
 
        <note>
         <para>
diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index eb1b698..8524dff 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -15441,6 +15441,13 @@ SELECT * FROM pg_ls_dir('.') WITH ORDINALITY AS t(ls,n);
       </row>
 
       <row>
+       <entry><literal><function>pg_current_logfile(<optional><type>text</></optional>)</function></literal></entry>
+       <entry><type>text</type></entry>
+       <entry>Primary log file name, or log in the requested format,
+       currently in use by the logging collector</entry>
+      </row>
+
+      <row>
        <entry><literal><function>pg_my_temp_schema()</function></literal></entry>
        <entry><type>oid</type></entry>
        <entry>OID of session's temporary schema, or 0 if none</entry>
@@ -15659,6 +15666,34 @@ SET search_path TO <replaceable>schema</> <optional>, <replaceable>schema</>, ..
    </para>
 
    <indexterm>
+    <primary>pg_current_logfile</primary>
+   </indexterm>
+
+   <indexterm>
+    <primary>Logging</primary>
+    <secondary>pg_current_logfile function</secondary>
+   </indexterm>
+
+   <para>
+    <function>pg_current_logfile</function> returns, as <type>text</type>,
+    the path of the log file(s) currently in use by the logging collector.
+    The path includes the <xref linkend="guc-log-directory"> directory
+    and the log file name.  Log collection must be enabled or the return value
+    is <literal>NULL</literal>.  When multiple log files exist, each in a
+    different format, <function>pg_current_logfile</function> called
+    without arguments returns the path of the file having the first format
+    found in the ordered list: <systemitem>stderr</>, <systemitem>csvlog</>.
+    <literal>NULL</literal> is returned when no log file has any of these
+    formats.  To request a specific file format supply, as <type>text</type>,
+    either <systemitem>csvlog</> or <systemitem>stderr</> as the value of the
+    optional parameter. The return value is <literal>NULL</literal> when the
+    log format requested is not a configured
+    <xref linkend="guc-log-destination">.
+    <function>pg_current_logfiles</function> reflects the contents of the
+    file <filename>current_logfiles</>.
+   </para>
+
+   <indexterm>
     <primary>pg_my_temp_schema</primary>
    </indexterm>
 
diff --git a/doc/src/sgml/storage.sgml b/doc/src/sgml/storage.sgml
index 5c52824..388ed34 100644
--- a/doc/src/sgml/storage.sgml
+++ b/doc/src/sgml/storage.sgml
@@ -61,6 +61,12 @@ Item
 </row>
 
 <row>
+ <entry><filename>current_logfiles</></entry>
+ <entry>File recording the log file(s) currently written to by the logging
+  collector</entry>
+</row>
+
+<row>
  <entry><filename>global</></entry>
  <entry>Subdirectory containing cluster-wide tables, such as
  <structname>pg_database</></entry>
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 31aade1..1d7f68b 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -1055,6 +1055,7 @@ REVOKE EXECUTE ON FUNCTION pg_xlog_replay_pause() FROM public;
 REVOKE EXECUTE ON FUNCTION pg_xlog_replay_resume() FROM public;
 REVOKE EXECUTE ON FUNCTION pg_rotate_logfile() FROM public;
 REVOKE EXECUTE ON FUNCTION pg_reload_conf() FROM public;
+REVOKE EXECUTE ON FUNCTION pg_current_logfile() FROM public;
 
 REVOKE EXECUTE ON FUNCTION pg_stat_reset() FROM public;
 REVOKE EXECUTE ON FUNCTION pg_stat_reset_shared(text) FROM public;
diff --git a/src/backend/postmaster/syslogger.c b/src/backend/postmaster/syslogger.c
index 13a0301..e6899c6 100644
--- a/src/backend/postmaster/syslogger.c
+++ b/src/backend/postmaster/syslogger.c
@@ -146,6 +146,7 @@ static char *logfile_getname(pg_time_t timestamp, const char *suffix);
 static void set_next_rotation_time(void);
 static void sigHupHandler(SIGNAL_ARGS);
 static void sigUsr1Handler(SIGNAL_ARGS);
+static void update_metainfo_datafile(void);
 
 
 /*
@@ -348,6 +349,13 @@ SysLoggerMain(int argc, char *argv[])
 				rotation_disabled = false;
 				rotation_requested = true;
 			}
+
+			/*
+			 * Force rewriting last log filename when reloading configuration,
+			 * even if rotation_requested is false, log_destination may have
+			 * been changed and we don't want to wait the next file rotation.
+			 */
+			update_metainfo_datafile();
 		}
 
 		if (Log_RotationAge > 0 && !rotation_disabled)
@@ -511,10 +519,16 @@ int
 SysLogger_Start(void)
 {
 	pid_t		sysloggerPid;
-	char	   *filename;
 
+	/*
+	 * Logging collector is not enabled. We don't know where messages are
+	 * logged.  Remove outdated file holding the current log filenames.
+	 */
 	if (!Logging_collector)
+	{
+		unlink(LOG_METAINFO_DATAFILE);
 		return 0;
+	}
 
 	/*
 	 * If first time through, create the pipe which will receive stderr
@@ -570,11 +584,15 @@ SysLogger_Start(void)
 	 * a time-based rotation.
 	 */
 	first_syslogger_file_time = time(NULL);
-	filename = logfile_getname(first_syslogger_file_time, NULL);
 
-	syslogFile = logfile_open(filename, "a", false);
+	if (last_file_name != NULL)
+		pfree(last_file_name);
+
+	last_file_name = logfile_getname(first_syslogger_file_time, NULL);
+
+	syslogFile = logfile_open(last_file_name, "a", false);
 
-	pfree(filename);
+	update_metainfo_datafile();
 
 #ifdef EXEC_BACKEND
 	switch ((sysloggerPid = syslogger_forkexec()))
@@ -1098,6 +1116,8 @@ open_csvlogfile(void)
 		pfree(last_csv_file_name);
 
 	last_csv_file_name = filename;
+
+	update_metainfo_datafile();
 }
 
 /*
@@ -1268,6 +1288,8 @@ logfile_rotate(bool time_based_rotation, int size_rotation_for)
 	if (csvfilename)
 		pfree(csvfilename);
 
+	update_metainfo_datafile();
+
 	set_next_rotation_time();
 }
 
@@ -1337,6 +1359,62 @@ set_next_rotation_time(void)
 	next_rotation_time = now;
 }
 
+/*
+ * Store the name of the file(s) where the log collector, when enabled, writes
+ * log messages.  Useful for finding the name(s) of the current log file(s)
+ * when there is time-based logfile rotation.  Filenames are stored in a
+ * temporary file and which is renamed into the final destination for
+ * atomicity.
+ */
+static void
+update_metainfo_datafile(void)
+{
+	FILE    *fh;
+
+	if (!(Log_destination & LOG_DESTINATION_STDERR) &&
+		!(Log_destination & LOG_DESTINATION_CSVLOG))
+	{
+		unlink(LOG_METAINFO_DATAFILE);
+		return;
+	}
+
+	if ((fh = logfile_open(LOG_METAINFO_DATAFILE_TMP, "w", true)) == NULL)
+		return;
+
+	if (last_file_name && (Log_destination & LOG_DESTINATION_STDERR))
+	{
+		if (fprintf(fh, "stderr %s\n", last_file_name) < 0)
+		{
+			ereport(LOG,
+					(errcode_for_file_access(),
+					errmsg("could not write stderr log file path \"%s\": %m",
+							LOG_METAINFO_DATAFILE_TMP)));
+			fclose(fh);
+			return;
+		}
+	}
+
+	if (last_csv_file_name && (Log_destination & LOG_DESTINATION_CSVLOG))
+	{
+		if (fprintf(fh, "csvlog %s\n", last_csv_file_name) < 0)
+		{
+			ereport(LOG,
+					(errcode_for_file_access(),
+					errmsg("could not write csvlog log file path \"%s\": %m",
+							LOG_METAINFO_DATAFILE_TMP)));
+			fclose(fh);
+			return;
+		}
+	}
+	fclose(fh);
+
+	if (rename(LOG_METAINFO_DATAFILE_TMP, LOG_METAINFO_DATAFILE) != 0)
+		ereport(LOG,
+				(errcode_for_file_access(),
+				errmsg("could not rename file \"%s\" to \"%s\": %m",
+					   LOG_METAINFO_DATAFILE_TMP, LOG_METAINFO_DATAFILE)));
+}
+
 /* --------------------------------
  *		signal handler routines
  * --------------------------------
diff --git a/src/backend/replication/basebackup.c b/src/backend/replication/basebackup.c
index 09ecc15..24d5d9f 100644
--- a/src/backend/replication/basebackup.c
+++ b/src/backend/replication/basebackup.c
@@ -27,6 +27,7 @@
 #include "nodes/pg_list.h"
 #include "pgtar.h"
 #include "pgstat.h"
+#include "postmaster/syslogger.h"
 #include "replication/basebackup.h"
 #include "replication/walsender.h"
 #include "replication/walsender_private.h"
@@ -148,6 +149,9 @@ static const char *excludeFiles[] =
 	/* Skip auto conf temporary file. */
 	PG_AUTOCONF_FILENAME ".tmp",
 
+	/* Skip current log file temporary file */
+	LOG_METAINFO_DATAFILE_TMP,
+
 	/*
 	 * If there's a backup_label or tablespace_map file, it belongs to a
 	 * backup started by the user with pg_start_backup().  It is *not* correct
diff --git a/src/backend/utils/adt/misc.c b/src/backend/utils/adt/misc.c
index 66d09bc..a40b27d 100644
--- a/src/backend/utils/adt/misc.c
+++ b/src/backend/utils/adt/misc.c
@@ -892,3 +892,110 @@ parse_ident(PG_FUNCTION_ARGS)
 
 	PG_RETURN_DATUM(makeArrayResult(astate, CurrentMemoryContext));
 }
+
+/*
+ * pg_current_logfile
+ *
+ * Report current log file used by log collector by scanning current_logfiles.
+ */
+Datum
+pg_current_logfile(PG_FUNCTION_ARGS)
+{
+	FILE    *fd;
+	char    lbuffer[MAXPGPATH];
+	char    *logfmt;
+	char    *log_filepath;
+	char    *log_format = lbuffer;
+
+	/* The log format parameter is optional */
+	if (PG_NARGS() == 0 || PG_ARGISNULL(0))
+		logfmt = NULL;
+	else
+	{
+		logfmt = text_to_cstring(PG_GETARG_TEXT_PP(0));
+
+		if (strcmp(logfmt, "stderr") != 0 && strcmp(logfmt, "csvlog") != 0)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+					 errmsg("log format \"%s\" is not supported", logfmt),
+					 errhint("The supported log formats are \"stderr\""
+									" and \"csvlog\".")));
+	}
+
+	fd = AllocateFile(LOG_METAINFO_DATAFILE, "r");
+	if (fd == NULL)
+	{
+		if (errno != ENOENT)
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m",
+						LOG_METAINFO_DATAFILE)));
+		PG_RETURN_NULL();
+	}
+
+	/*
+	 * Read the file to gather current log filename(s) registered
+	 * by the syslogger.
+	 */
+	while (fgets(lbuffer, sizeof(lbuffer), fd) != NULL)
+	{
+		/* Check for a read error. */
+		if (ferror(fd))
+		{
+			int save_errno = errno;
+			FreeFile(fd);
+			errno = save_errno;
+
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m",
+							LOG_METAINFO_DATAFILE)));
+		}
+
+		/*
+		 * Extract log format and log file path from the line;
+		 * lbuffer == log_format, they share storage.
+		 */
+		log_filepath = strchr(lbuffer, ' ');
+		if (log_filepath == NULL)
+		{
+			/*
+			 * Corrupted data found, return NULL to the caller and
+			 * inform him on the situation.
+			 */
+			ereport(WARNING,
+					(errcode(ERRCODE_INTERNAL_ERROR),
+					 errmsg("corrupted data found in \"%s\"",
+							LOG_METAINFO_DATAFILE)));
+			break;
+		}
+
+		*log_filepath = '\0';
+		log_filepath++;
+		log_filepath[strcspn(log_filepath, "\n")] = '\0';
+
+		if (logfmt == NULL || strcmp(logfmt, log_format) == 0)
+		{
+			FreeFile(fd);
+			PG_RETURN_TEXT_P(cstring_to_text(log_filepath));
+		}
+	}
+
+	/* Close the current log filename file. */
+	FreeFile(fd);
+
+	PG_RETURN_NULL();
+}
+
+/*
+ * Report current log file used by log collector (1 argument version)
+ *
+ * note: this wrapper is necessary to pass the sanity check in opr_sanity,
+ * which checks that all built-in functions that share the implementing C
+ * function take the same number of arguments
+ */
+Datum
+pg_current_logfile_1arg(PG_FUNCTION_ARGS)
+{
+	return pg_current_logfile(fcinfo);
+}
diff --git a/src/bin/pg_basebackup/t/010_pg_basebackup.pl b/src/bin/pg_basebackup/t/010_pg_basebackup.pl
index 2c5a365..f9af3fe 100644
--- a/src/bin/pg_basebackup/t/010_pg_basebackup.pl
+++ b/src/bin/pg_basebackup/t/010_pg_basebackup.pl
@@ -4,7 +4,7 @@ use Cwd;
 use Config;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 72;
+use Test::More tests => 73;
 
 program_help_ok('pg_basebackup');
 program_version_ok('pg_basebackup');
@@ -56,7 +56,7 @@ close CONF;
 $node->restart;
 
 # Write some files to test that they are not copied.
-foreach my $filename (qw(backup_label tablespace_map postgresql.auto.conf.tmp))
+foreach my $filename (qw(backup_label tablespace_map postgresql.auto.conf.tmp current_logfiles.tmp))
 {
 	open FILE, ">>$pgdata/$filename";
 	print FILE "DONOTCOPY";
@@ -83,7 +83,7 @@ foreach my $dirname (qw(pg_dynshmem pg_notify pg_replslot pg_serial pg_snapshots
 }
 
 # These files should not be copied.
-foreach my $filename (qw(postgresql.auto.conf.tmp postmaster.opts postmaster.pid tablespace_map))
+foreach my $filename (qw(postgresql.auto.conf.tmp postmaster.opts postmaster.pid tablespace_map current_logfiles.tmp))
 {
 	ok(! -f "$tempdir/backup/$filename", "$filename not copied");
 }
diff --git a/src/include/catalog/pg_proc.h b/src/include/catalog/pg_proc.h
index 1a0eba3..aeceb33 100644
--- a/src/include/catalog/pg_proc.h
+++ b/src/include/catalog/pg_proc.h
@@ -3187,6 +3187,10 @@ DATA(insert OID = 2621 ( pg_reload_conf			PGNSP PGUID 12 1 0 0 0 f f f f t f v s
 DESCR("reload configuration files");
 DATA(insert OID = 2622 ( pg_rotate_logfile		PGNSP PGUID 12 1 0 0 0 f f f f t f v s 0 0 16 "" _null_ _null_ _null_ _null_ _null_ pg_rotate_logfile _null_ _null_ _null_ ));
 DESCR("rotate log file");
+DATA(insert OID = 3800 ( pg_current_logfile             PGNSP PGUID 12 1 0 0 0 f f f f f f v s 0 0 25 "" _null_ _null_ _null_ _null_ _null_ pg_current_logfile _null_ _null_ _null_ ));
+DESCR("current logging collector file location");
+DATA(insert OID = 3801 ( pg_current_logfile             PGNSP PGUID 12 1 0 0 0 f f f f f f v s 1 0 25 "25" _null_ _null_ _null_ _null_ _null_ pg_current_logfile_1arg _null_ _null_ _null_ ));
+DESCR("current logging collector file location");
 
 DATA(insert OID = 2623 ( pg_stat_file		PGNSP PGUID 12 1 0 0 0 f f f f t f v s 1 0 2249 "25" "{25,20,1184,1184,1184,1184,16}" "{i,o,o,o,o,o,o}" "{filename,size,access,modification,change,creation,isdir}" _null_ _null_ pg_stat_file_1arg _null_ _null_ _null_ ));
 DESCR("get information about file");
diff --git a/src/include/postmaster/syslogger.h b/src/include/postmaster/syslogger.h
index c187a5f..ebe3247 100644
--- a/src/include/postmaster/syslogger.h
+++ b/src/include/postmaster/syslogger.h
@@ -87,4 +87,11 @@ extern void write_syslogger_file(const char *buffer, int count, int dest);
 extern void SysLoggerMain(int argc, char *argv[]) pg_attribute_noreturn();
 #endif
 
+/*
+ * Name of files saving meta-data information about the log
+ * files currently in use by the system logging process
+ */
+#define LOG_METAINFO_DATAFILE  "current_logfiles"
+#define LOG_METAINFO_DATAFILE_TMP  LOG_METAINFO_DATAFILE ".tmp"
+
 #endif   /* _SYSLOGGER_H */
-- 
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