Re: [HACKERS] serverlog function (log_destination file)

Magnus Hagander wrote:

>Specifically about the logs, I still think there is a lot of value to
>being able to read the logs remotely even if you can't restart
>postmaster.
>
Since I believe that retrieving the logs easily without server file
access is a feature that's welcomed by many users, here's my proposal.

The attached diff will
- add a guc-variable log_filename
- extend log_destination to accept the keyword 'file'
- elog to that file if configured
- provide two functions pg_logfile_length() and pg_logfile to obtain the
contents.

int4 pg_logfile_length()
cstring pg_logfile(int4 size, int4 position)
size (may be null meaning max) is the chunk size (max: currently 50000)
position (may be null meaning -size) is the start position; positive
counting from log file start, negative from end.


Regards,
Andreas

Index: backend/postmaster/postmaster.c
===================================================================
RCS file: /projects/cvsroot/pgsql-server/src/backend/postmaster/postmaster.c,v
retrieving revision 1.402
diff -u -r1.402 postmaster.c
--- backend/postmaster/postmaster.c    3 Jun 2004 02:08:03 -0000    1.402
+++ backend/postmaster/postmaster.c    8 Jun 2004 18:07:30 -0000
@@ -532,6 +532,9 @@
     /* If timezone is not set, determine what the OS uses */
     pg_timezone_initialize();

+    /* open alternate logfile, if any */
+    LogFileOpen();
+
 #ifdef EXEC_BACKEND
     write_nondefault_variables(PGC_POSTMASTER);
 #endif
Index: backend/storage/ipc/ipc.c
===================================================================
RCS file: /projects/cvsroot/pgsql-server/src/backend/storage/ipc/ipc.c,v
retrieving revision 1.87
diff -u -r1.87 ipc.c
--- backend/storage/ipc/ipc.c    12 Dec 2003 18:45:09 -0000    1.87
+++ backend/storage/ipc/ipc.c    8 Jun 2004 18:07:31 -0000
@@ -111,6 +111,8 @@
                               on_proc_exit_list[on_proc_exit_index].arg);

     elog(DEBUG3, "exit(%d)", code);
+
+    LogFileClose();
     exit(code);
 }

Index: backend/utils/adt/misc.c
===================================================================
RCS file: /projects/cvsroot/pgsql-server/src/backend/utils/adt/misc.c,v
retrieving revision 1.34
diff -u -r1.34 misc.c
--- backend/utils/adt/misc.c    2 Jun 2004 21:29:29 -0000    1.34
+++ backend/utils/adt/misc.c    8 Jun 2004 18:07:36 -0000
@@ -103,3 +103,64 @@
 {
     PG_RETURN_INT32(pg_signal_backend(PG_GETARG_INT32(0),SIGINT));
 }
+
+Datum pg_logfile_length(PG_FUNCTION_ARGS)
+{
+    extern FILE *logfile; // in elog.c
+
+    if (logfile)
+        PG_RETURN_INT32(ftell(logfile));
+    PG_RETURN_INT32(0);
+}
+
+
+#define MAXLOGFILECHUNK 50000
+Datum pg_logfile(PG_FUNCTION_ARGS)
+{
+    size_t size=MAXLOGFILECHUNK;
+    char *buf=0;
+    size_t nbytes;
+
+    char *filename = LogFileName();
+    if (filename)
+    {
+        if (!PG_ARGISNULL(0))
+            size = PG_GETARG_INT32(0);
+        if (size > MAXLOGFILECHUNK)
+        {
+            size = MAXLOGFILECHUNK;
+            ereport(WARNING,
+                    (errcode(ERRCODE_OUT_OF_MEMORY),
+                     errmsg("Maximum size is %d.", MAXLOGFILECHUNK)));
+        }
+
+        FILE *f=fopen(filename, "r");
+        if (f)
+        {
+            if (PG_ARGISNULL(1))
+                fseek(f, -size, SEEK_END);
+            else
+            {
+                long pos = PG_GETARG_INT32(1);
+                if (pos >= 0)
+                    fseek(f, pos, SEEK_SET);
+                else
+                    fseek(f, pos, SEEK_END);
+            }
+            buf = palloc(size+1);
+            nbytes = fread(buf, 1, size, f);
+            buf[nbytes] = 0;
+
+            fclose(f);
+        }
+        else
+        {
+            ereport(WARNING,
+                    (errcode(ERRCODE_NO_DATA),
+                     errmsg("Could not open log file %s.", filename)));
+        }
+        free(filename);
+    }
+
+    PG_RETURN_CSTRING(buf);
+}
Index: backend/utils/error/elog.c
===================================================================
RCS file: /projects/cvsroot/pgsql-server/src/backend/utils/error/elog.c,v
retrieving revision 1.140
diff -u -r1.140 elog.c
--- backend/utils/error/elog.c    3 Jun 2004 02:08:04 -0000    1.140
+++ backend/utils/error/elog.c    8 Jun 2004 18:07:39 -0000
@@ -71,8 +71,10 @@
 PGErrorVerbosity Log_error_verbosity = PGERROR_VERBOSE;
 char       *Log_line_prefix = NULL; /* format for extra log line info */
 unsigned int Log_destination = LOG_DESTINATION_STDERR;
+char *Log_filename = NULL;

 bool in_fatal_exit = false;
+FILE *logfile = NULL;

 #ifdef HAVE_SYSLOG
 char       *Syslog_facility;    /* openlog() parameters */
@@ -936,6 +938,69 @@


 /*
+ * Name of configured log file, or NULL
+ * must be freed after usage
+ */
+char*
+LogFileName(void)
+{
+    if (Log_filename && (Log_destination & LOG_DESTINATION_FILE))
+    {
+        if (is_absolute_path(Log_filename))
+            return strdup(Log_filename);
+        else
+        {
+            char *buf = malloc(strlen(DataDir) + strlen(Log_filename) +2);
+            if (!buf)
+                ereport(FATAL,
+                        (errcode(ERRCODE_OUT_OF_MEMORY),
+                         errmsg("out of memory")));
+
+            sprintf(buf, "%s/%s", DataDir, Log_filename);
+
+            return buf;
+        }
+    }
+    return NULL;
+}
+
+
+/*
+ * Open log file, if configured.
+ */
+void
+LogFileOpen(void)
+{
+    char *filename = LogFileName();
+
+    if (filename)
+    {
+        LogFileClose();
+
+        logfile = fopen(filename, "at");
+
+        if (!logfile)
+            ereport(WARNING,
+                    (errcode(ERRCODE_CONFIG_FILE_ERROR),
+                     errmsg("could not open log file %s", filename)));
+
+        free(filename);
+    }
+}
+
+
+/*
+ * Close log file, if open.
+ */
+void
+LogFileClose(void)
+{
+    if (logfile)
+        fclose(logfile);
+    logfile = NULL;
+}
+
+/*
  * Initialization of error output file
  */
 void
@@ -1445,6 +1510,11 @@
     if ((Log_destination & LOG_DESTINATION_STDERR) || whereToSendOutput == Debug)
     {
         fprintf(stderr, "%s", buf.data);
+    }
+
+    if (logfile && (Log_destination & LOG_DESTINATION_FILE))
+    {
+        fprintf(logfile, "%s", buf.data);
     }

     pfree(buf.data);
Index: backend/utils/misc/guc.c
===================================================================
RCS file: /projects/cvsroot/pgsql-server/src/backend/utils/misc/guc.c,v
retrieving revision 1.210
diff -u -r1.210 guc.c
--- backend/utils/misc/guc.c    30 May 2004 23:40:38 -0000    1.210
+++ backend/utils/misc/guc.c    8 Jun 2004 18:07:47 -0000
@@ -76,6 +76,8 @@
 static const char *assign_log_destination(const char *value,
                 bool doit, GucSource source);

+extern char *Log_filename;
+
 #ifdef HAVE_SYSLOG
 extern char *Syslog_facility;
 extern char *Syslog_ident;
@@ -1644,13 +1646,23 @@
     {
         {"log_destination", PGC_POSTMASTER, LOGGING_WHERE,
          gettext_noop("Sets the target for log output."),
-         gettext_noop("Valid values are combinations of stderr, syslog "
+         gettext_noop("Valid values are combinations of stderr, file, syslog "
                       "and eventlog, depending on platform."),
          GUC_LIST_INPUT | GUC_REPORT
         },
         &log_destination_string,
         "stderr", assign_log_destination, NULL
     },
+    {
+        {"log_filename", PGC_POSTMASTER, LOGGING_WHERE,
+         gettext_noop("Sets the target filename for log output."),
+         gettext_noop("May be specified as relative to the cluster directory "
+                      "or as absolute path."),
+         GUC_LIST_INPUT | GUC_REPORT
+        },
+        &Log_filename,
+        "postgresql.log", NULL, NULL
+    },

 #ifdef HAVE_SYSLOG
     {
@@ -4775,6 +4787,8 @@

         if (pg_strcasecmp(tok,"stderr") == 0)
             newlogdest |= LOG_DESTINATION_STDERR;
+        else if (pg_strcasecmp(tok,"file") == 0)
+            newlogdest |= LOG_DESTINATION_FILE;
 #ifdef HAVE_SYSLOG
         else if (pg_strcasecmp(tok,"syslog") == 0)
             newlogdest |= LOG_DESTINATION_SYSLOG;
Index: backend/utils/misc/postgresql.conf.sample
===================================================================
RCS file: /projects/cvsroot/pgsql-server/src/backend/utils/misc/postgresql.conf.sample,v
retrieving revision 1.113
diff -u -r1.113 postgresql.conf.sample
--- backend/utils/misc/postgresql.conf.sample    7 Apr 2004 05:05:50 -0000    1.113
+++ backend/utils/misc/postgresql.conf.sample    8 Jun 2004 18:07:48 -0000
@@ -147,9 +147,10 @@

 # - Where to Log -

-#log_destination = 'stderr'    # Valid values are combinations of stderr,
+#log_destination = 'stderr'    # Valid values are combinations of stderr, file,
                                 # syslog and eventlog, depending on
                                 # platform.
+#log_filename = 'pgsql.log'
 #syslog_facility = 'LOCAL0'
 #syslog_ident = 'postgres'

Index: include/catalog/pg_proc.h
===================================================================
RCS file: /projects/cvsroot/pgsql-server/src/include/catalog/pg_proc.h,v
retrieving revision 1.334
diff -u -r1.334 pg_proc.h
--- include/catalog/pg_proc.h    2 Jun 2004 21:29:29 -0000    1.334
+++ include/catalog/pg_proc.h    8 Jun 2004 18:08:03 -0000
@@ -3588,6 +3588,12 @@
 DATA(insert OID = 2243 ( bit_or                           PGNSP PGUID 12 t f f f i 1 1560 "1560" _null_
aggregate_dummy- _null_)); 
 DESCR("bitwise-or bit aggregate");

+DATA(insert OID = 2550(  pg_logfile_length               PGNSP PGUID 12 f f f f v 0 23 "" _null_ pg_logfile_length -
_null_)); 
+DESCR("length of log file");
+DATA(insert OID = 2551(  pg_logfile                       PGNSP PGUID 12 f f f f v 2 2275 "23 23" _null_ pg_logfile -
_null_)); 
+DESCR("return log file contents");
+
+
 /*
  * Symbolic values for provolatile column: these indicate whether the result
  * of a function is dependent *only* on the values of its explicit arguments,
Index: include/utils/builtins.h
===================================================================
RCS file: /projects/cvsroot/pgsql-server/src/include/utils/builtins.h,v
retrieving revision 1.241
diff -u -r1.241 builtins.h
--- include/utils/builtins.h    2 Jun 2004 21:29:29 -0000    1.241
+++ include/utils/builtins.h    8 Jun 2004 18:08:05 -0000
@@ -356,6 +356,8 @@
 extern Datum current_database(PG_FUNCTION_ARGS);
 extern Datum pg_terminate_backend(PG_FUNCTION_ARGS);
 extern Datum pg_cancel_backend(PG_FUNCTION_ARGS);
+extern Datum pg_logfile_length(PG_FUNCTION_ARGS);
+extern Datum pg_logfile(PG_FUNCTION_ARGS);

 /* not_in.c */
 extern Datum int4notin(PG_FUNCTION_ARGS);
Index: include/utils/elog.h
===================================================================
RCS file: /projects/cvsroot/pgsql-server/src/include/utils/elog.h,v
retrieving revision 1.68
diff -u -r1.68 elog.h
--- include/utils/elog.h    5 Apr 2004 03:02:10 -0000    1.68
+++ include/utils/elog.h    8 Jun 2004 18:08:06 -0000
@@ -182,8 +182,12 @@
 #define LOG_DESTINATION_STDERR   1
 #define LOG_DESTINATION_SYSLOG   2
 #define LOG_DESTINATION_EVENTLOG 4
+#define LOG_DESTINATION_FILE     8

 /* Other exported functions */
 extern void DebugFileOpen(void);
+extern char *LogFileName(void);
+extern void LogFileOpen(void);
+extern void LogFileClose(void);

 #endif   /* ELOG_H */