fix: timezone handling in logging, so local timezone is always used

Author: sanikolaev

manual/english/Server_settings/Searchd.md

@@ -507,14 +507,16 @@ expansion_phrase_warning = 1
 
 This setting specifies whether timed grouping in API and SQL will be calculated in the local timezone or in UTC. It is optional, with a default value of 0 (meaning 'local timezone').
 
-By default, all 'group by time' expressions (like group by day, week, month, and year in API, also group by day, month, year, yearmonth, yearmonthday in SQL) are done using local time. For example, if you have documents with attributes timed `13:00 utc` and `15:00 utc`, in the case of grouping, they both will fall into facility groups according to your local timezone setting. If you live in `utc`, it will be one day, but if you live in `utc+10`, then these documents will be matched into different `group by day` facility groups (since 13:00 utc in UTC+10 timezone is 23:00 local time, but 15:00 is 01:00 of the next day). Sometimes such behavior is unacceptable, and it is desirable to make time grouping not dependent on timezone. You can run the server with a defined global TZ environment variable, but it will affect not only grouping but also timestamping in the logs, which may be undesirable as well. Switching 'on' this option (either in config or using [SET global](../Server_settings/Setting_variables_online.md#SET) statement in SQL) will cause all time grouping expressions to be calculated in UTC, leaving the rest of time-depentend functions (i.e. logging of the server) in local TZ.
+By default, all 'group by time' expressions (like group by day, week, month, and year in API, also group by day, month, year, yearmonth, yearmonthday in SQL) are done using local time. For example, if you have documents with attributes timed `13:00 utc` and `15:00 utc`, in the case of grouping, they both will fall into facility groups according to your local timezone setting. If you live in `utc`, it will be one day, but if you live in `utc+10`, then these documents will be matched into different `group by day` facility groups (since 13:00 utc in UTC+10 timezone is 23:00 local time, but 15:00 is 01:00 of the next day). Sometimes such behavior is unacceptable, and it is desirable to make time grouping not dependent on timezone. You can run the server with a defined global TZ environment variable to affect time functions, but note that logging always uses the actual system local timezone (from `/etc/localtime`) and is not affected by TZ. Switching 'on' this option (either in config or using [SET global](../Server_settings/Setting_variables_online.md#SET) statement in SQL) will cause all time grouping expressions to be calculated in UTC, leaving the rest of time-dependent functions (i.e. logging of the server) in local TZ.
 
 
 ### timezone
 
 This setting specifies the timezone to be used by date/time-related functions. By default, the local timezone is used, but you can specify a different timezone in IANA format (e.g., `Europe/Amsterdam`).
 
-Note that this setting has no impact on logging, which always operates in the local timezone.
+Note that this setting has no impact on logging, which always operates in the actual system local timezone (from `/etc/localtime`), regardless of this setting or the TZ environment variable.
+
+The TZ environment variable works similarly to this setting: if set, it affects date/time-related functions (like `NOW()`, `CURTIME()`, etc.), but does not affect logging. Logging always uses the actual system local timezone to ensure timestamps reflect the real local time.
 
 Also, note that if `grouping_in_utc` is used, the 'group by time' function will still use UTC, while other date/time-related functions will use the specified timezone. Overall, it is not recommended to mix `grouping_in_utc` and `timezone`.
 

src/datetime.cpp

@@ -34,19 +34,10 @@ static CSphString DetermineLocalTimeZoneName ( CSphString & sWarning )
 	if ( szTZDefault )
 		sTimeZoneFile = szTZDefault;
 
-	const char * szTZ = getenv("TZ");
-	if ( szTZ )
-	{
-		sPrefix.SetSprintf ( "%s TZ='%s'", sPrefix.cstr(), szTZ );
-
-		if ( *szTZ==':' )
-			++szTZ;
-
-		if ( *szTZ )
-			sTimeZoneFile = szTZ;
-	}
-	else
-		sPrefix.SetSprintf ( "%s '%s'", sPrefix.cstr(), sTimeZoneFile.cstr() );
+	// Note: We intentionally ignore TZ environment variable here because
+	// logging should always use the actual system local timezone, not TZ
+	// TZ is meant for application-level timezone overrides, not system timezone
+	sPrefix.SetSprintf ( "%s '%s'", sPrefix.cstr(), sTimeZoneFile.cstr() );
 
 	CSphString sTimeZoneDir = "/usr/share/zoneinfo/";
 	const char * szTZDIR = getenv("TZDIR");
@@ -116,6 +107,9 @@ static void SetTimeZoneLocal ( StrVec_t & dWarnings )
 	CSphString sDirName;
 	sDirName.SetSprintf ( "%s/tzdata", GET_FULL_SHARE_DIR() );
 
+	// Save TZ env var before we potentially unset it
+	const char * szTZ = getenv("TZ");
+
 #if _WIN32
 	_putenv_s ( "TZDIR", sDirName.cstr() );
 
@@ -129,17 +123,40 @@ static void SetTimeZoneLocal ( StrVec_t & dWarnings )
 
 	sZone = FixupZoneName(sZone);
 
-	setenv ( "TZDIR", sDirName.cstr(), 1 );
+	// Always use cctz::local_time_zone() to get the actual system local timezone
+	// Temporarily unset TZ to ensure we get the actual system local timezone, not TZ
+	// This ensures logging always uses the real local timezone regardless of TZ env var
+	if ( szTZ )
+		unsetenv("TZ");
+	g_hTimeZoneLocal = cctz::local_time_zone();
+	if ( szTZ )
+		setenv("TZ", szTZ, 1);
+#endif
 
-	if ( !cctz::load_time_zone ( sZone.cstr(), &g_hTimeZoneLocal ) )
+	// For time functions: use TZ if set, otherwise use local timezone
+	// For logging: always use local timezone (g_hTimeZoneLocal)
+	setenv ( "TZDIR", sDirName.cstr(), 1 );
+	if ( szTZ && *szTZ )
 	{
-		sWarning.SetSprintf ( "Unable to load local time zone '%s' from '%s' dir", sZone.cstr(), sDirName.cstr() );
-		dWarnings.Add(sWarning);
-		g_hTimeZoneLocal = g_hTimeZoneUTC;
+		// Skip leading colon if present
+		const char * szTZName = szTZ;
+		if ( *szTZName == ':' )
+			++szTZName;
+		if ( *szTZName && cctz::load_time_zone ( szTZName, &g_hTimeZone ) )
+		{
+			// Successfully loaded TZ timezone for time functions
+		}
+		else
+		{
+			// TZ set but invalid, fall back to local timezone
+			g_hTimeZone = g_hTimeZoneLocal;
+		}
+	}
+	else
+	{
+		// No TZ set, use local timezone for time functions
+		g_hTimeZone = g_hTimeZoneLocal;
 	}
-#endif
-
-	g_hTimeZone = g_hTimeZoneLocal;
 	CheckForUTC();
 }