Re: [Proposal] Adding Log File Capability to pg_createsubscriber

On Tue, Feb 24, 2026, at 8:55 PM, Gyan Sreejith wrote:
> I have made the changes you suggested and have attached the patch below. 
>

[Avoid top-posting ...]

I took another look at this patch. Comments are below:

+/*
+ * Open a new logfile with proper permissions.
+ * From src/backend/postmaster/syslogger.c
+ */
+static FILE *
+logfile_open(const char *filename, const char *mode)
+{

Don't duplicate code. If you are reusing a function, my advice is to move it to
src/common. You can always use "ifdef FRONTEND" to use the appropriate log
message (elog/ereport vs pg_error, for example).

-	 * XXX this code was extracted from BootStrapXLOG().
+	 * XXX this code was extracted from BootStrapXpg_log_info().

This is a typo.

+			case 'l':
+				{
+					char		timestamp[128];
+					struct timeval tval;
+					time_t		now;
+					struct tm	tmbuf;

I would expect to have this code in a function. That's the pattern it is using.

+					strftime(timestamp, sizeof(timestamp), "%Y-%m-%d-%H-%M-%S", localtime_r(&now, &tmbuf));
+					/* append microseconds */
+					snprintf(timestamp + strlen(timestamp), sizeof(timestamp) - strlen(timestamp),
+							 ".%06u", (unsigned int) (tval.tv_usec));
+					log_timestamp = pg_strdup(timestamp);

Do we really need microseconds? I would say milliseconds is sufficient. I
suggest to remove the dash (-); it is using a different style from existing
code (pg_upgrade).

+					opt.log_dir = pg_strdup(optarg);
+					canonicalize_path(opt.log_dir);

You didn't have a check for long path. It is not a good idea in general. See
MAXPGPATH examples. It would be a good idea if the path are restricted to
MAXPGPATH length.

+						if (errno == ENOENT)
+						{
+							if (mkdir(opt.log_dir, S_IRWXU) == 0)
+								pg_log_info("log directory created");
+							else if (errno == EACCES)
+								pg_fatal("permission denied trying to create log directory \"%s\": %m", opt.log_dir);
+							else
+								pg_fatal("could not create log directory \"%s\": %m", opt.log_dir);
+						}
+						else if (errno == EACCES)
+							pg_fatal("permission denied trying to access directory \"%s\": %m", opt.log_dir);
+						else
+							pg_fatal("could not access directory \"%s\": %m", opt.log_dir);

The "permission denied" is redundant here because it will be in %m. Instead, I
suggest that you use

  could not create directory \"%s\": %m

The main advantage is that this sentence is already available. It avoids
translation effort.

+#undef pg_log_info
+#define pg_log_info(...) do{\
+	if (internal_log_file_fp != NULL) \
+		internal_log_file_write(__VA_ARGS__); \
+	else \
+		pg_log_generic(PG_LOG_INFO,PG_LOG_PRIMARY,__VA_ARGS__);\
+} while(0)

I don't like the fact that internal_log_file_fp is not declared before this
#define.

One of the arguments to have this feature was that pg_createsubscriber mixes the
server and tool messages. Couldn't we fix it adding "marks" on the output saying
the server log messages starts here and the server log messages ends here?


-- 
Euler Taveira
EDB   https://www.enterprisedb.com/