PostgreSQL

+
`+current_logfiles+` is recreated when a new log file is created as an effect of rotation, and when `+log_destination+` is reloaded. It is removed when neither [.systemitem]#stderr# nor [.systemitem]#csvlog# are included in `+log_destination+`, and when the logging collector is disabled.
+
[NOTE]
====
==== Note

On most Unix systems, you will need to alter the configuration of your system's syslog daemon in order to make use of the [.systemitem]#syslog# option for `+log_destination+`. PostgreSQL can log to syslog facilities `+LOCAL0+` through `+LOCAL7+` (see link:runtime-config-logging.html#GUC-SYSLOG-FACILITY[syslog_facility]), but the default syslog configuration on most platforms will discard all such messages. You will need to add something like:

to the syslog daemon's configuration file to make it work.

  On Windows, when you use the `+eventlog+` option for `+log_destination+`, you should register an event source and its library with the operating system so that the Windows Event Viewer can display event log messages cleanly. See link:event-log-registration.html[Section 18.11] for details.
  ====
[.term]#`+logging_collector+` (`+boolean+`) ::
  This parameter enables the _logging collector_, which is a background process that captures log messages sent to [.systemitem]#stderr# and redirects them into log files. This approach is often more useful than logging to syslog, since some types of messages might not appear in syslog output. (One common example is dynamic-linker failure messages; another is error messages produced by scripts such as `+archive_command+`.) This parameter can only be set at server start.
  +
  [NOTE]
  ====
  ==== Note

It is possible to log to [.systemitem]#stderr# without using the logging collector; the log messages will just go to wherever the server's [.systemitem]#stderr# is directed. However, that method is only suitable for low log volumes, since it provides no convenient way to rotate log files. Also, on some platforms not using the logging collector can result in lost or garbled log output, because multiple processes writing concurrently to the same log file can overwrite each other's output.
====
+
[NOTE]
====
==== Note

  The logging collector is designed to never lose messages. This means that in case of extremely high load, server processes could be blocked while trying to send additional log messages when the collector has fallen behind. In contrast, syslog prefers to drop messages if it cannot write them, which means it may fail to log some messages in such cases but it will not block the rest of the system.
  ====
[.term]#`+log_directory+` (`+string+`) ::
  When `+logging_collector+` is enabled, this parameter determines the directory in which log files will be created. It can be specified as an absolute path, or relative to the cluster data directory. This parameter can only be set in the `+postgresql.conf+` file or on the server command line. The default is `+log+`.
[.term]#`+log_filename+` (`+string+`) ::
  When `+logging_collector+` is enabled, this parameter sets the file names of the created log files. The value is treated as a `+strftime+` pattern, so `+%+`-escapes can be used to specify time-varying file names. (Note that if there are any time-zone-dependent `+%+`-escapes, the computation is done in the zone specified by link:runtime-config-logging.html#GUC-LOG-TIMEZONE[log_timezone].) The supported `+%+`-escapes are similar to those listed in the Open Group's https://pubs.opengroup.org/onlinepubs/009695399/functions/strftime.html[strftime] specification. Note that the system's `+strftime+` is not used directly, so platform-specific (nonstandard) extensions do not work. The default is `+postgresql-%Y-%m-%d_%H%M%S.log+`.
  +
  If you specify a file name without escapes, you should plan to use a log rotation utility to avoid eventually filling the entire disk. In releases prior to 8.4, if no `+%+` escapes were present, PostgreSQL would append the epoch of the new log file's creation time, but this is no longer the case.
  +
  If CSV-format output is enabled in `+log_destination+`, `+.csv+` will be appended to the timestamped log file name to create the file name for CSV-format output. (If `+log_filename+` ends in `+.log+`, the suffix is replaced instead.)
  +
  This parameter can only be set in the `+postgresql.conf+` file or on the server command line.
[.term]#`+log_file_mode+` (`+integer+`) ::
  On Unix systems this parameter sets the permissions for log files when `+logging_collector+` is enabled. (On Microsoft Windows this parameter is ignored.) The parameter value is expected to be a numeric mode specified in the format accepted by the `+chmod+` and `+umask+` system calls. (To use the customary octal format the number must start with a `+0+` (zero).)
  +
  The default permissions are `+0600+`, meaning only the server owner can read or write the log files. The other commonly useful setting is `+0640+`, allowing members of the owner's group to read the files. Note however that to make use of such a setting, you'll need to alter link:runtime-config-logging.html#GUC-LOG-DIRECTORY[log_directory] to store the files somewhere outside the cluster data directory. In any case, it's unwise to make the log files world-readable, since they might contain sensitive data.
  +
  This parameter can only be set in the `+postgresql.conf+` file or on the server command line.
[.term]#`+log_rotation_age+` (`+integer+`) ::
  When `+logging_collector+` is enabled, this parameter determines the maximum lifetime of an individual log file. After this many minutes have elapsed, a new log file will be created. Set to zero to disable time-based creation of new log files. This parameter can only be set in the `+postgresql.conf+` file or on the server command line.
[.term]#`+log_rotation_size+` (`+integer+`) ::
  When `+logging_collector+` is enabled, this parameter determines the maximum size of an individual log file. After this many kilobytes have been emitted into a log file, a new log file will be created. Set to zero to disable size-based creation of new log files. This parameter can only be set in the `+postgresql.conf+` file or on the server command line.
[.term]#`+log_truncate_on_rotation+` (`+boolean+`) ::
  When `+logging_collector+` is enabled, this parameter will cause PostgreSQL to truncate (overwrite), rather than append to, any existing log file of the same name. However, truncation will occur only when a new file is being opened due to time-based rotation, not during server startup or size-based rotation. When off, pre-existing files will be appended to in all cases. For example, using this setting in combination with a `+log_filename+` like `+postgresql-%H.log+` would result in generating twenty-four hourly log files and then cyclically overwriting them. This parameter can only be set in the `+postgresql.conf+` file or on the server command line.
  +
  Example: To keep 7 days of logs, one log file per day named `+server_log.Mon+`, `+server_log.Tue+`, etc, and automatically overwrite last week's log with this week's log, set `+log_filename+` to `+server_log.%a+`, `+log_truncate_on_rotation+` to `+on+`, and `+log_rotation_age+` to `+1440+`.
  +
  Example: To keep 24 hours of logs, one log file per hour, but also rotate sooner if the log file size exceeds 1GB, set `+log_filename+` to `+server_log.%H%M+`, `+log_truncate_on_rotation+` to `+on+`, `+log_rotation_age+` to `+60+`, and `+log_rotation_size+` to `+1000000+`. Including `+%M+` in `+log_filename+` allows any size-driven rotations that might occur to select a file name different from the hour's initial file name.
[.term]#`+syslog_facility+` (`+enum+`) ::
  When logging to syslog is enabled, this parameter determines the syslog [.quote]#“[.quote]#facility#”# to be used. You can choose from `+LOCAL0+`, `+LOCAL1+`, `+LOCAL2+`, `+LOCAL3+`, `+LOCAL4+`, `+LOCAL5+`, `+LOCAL6+`, `+LOCAL7+`; the default is `+LOCAL0+`. See also the documentation of your system's syslog daemon. This parameter can only be set in the `+postgresql.conf+` file or on the server command line.
[.term]#`+syslog_ident+` (`+string+`) ::
  When logging to syslog is enabled, this parameter determines the program name used to identify PostgreSQL messages in syslog logs. The default is `+postgres+`. This parameter can only be set in the `+postgresql.conf+` file or on the server command line.
[.term]#`+syslog_sequence_numbers+` (`+boolean+`) ::
  When logging to syslog and this is on (the default), then each message will be prefixed by an increasing sequence number (such as `+[2]+`). This circumvents the [.quote]#“[.quote]#--- last message repeated N times ---#”# suppression that many syslog implementations perform by default. In more modern syslog implementations, repeated message suppression can be configured (for example, `+$RepeatedMsgReduction+` in rsyslog), so this might not be necessary. Also, you could turn this off if you actually want to suppress repeated messages.
  +
  This parameter can only be set in the `+postgresql.conf+` file or on the server command line.
[.term]#`+syslog_split_messages+` (`+boolean+`) ::
  When logging to syslog is enabled, this parameter determines how messages are delivered to syslog. When on (the default), messages are split by lines, and long lines are split so that they will fit into 1024 bytes, which is a typical size limit for traditional syslog implementations. When off, PostgreSQL server log messages are delivered to the syslog service as is, and it is up to the syslog service to cope with the potentially bulky messages.
  +
  If syslog is ultimately logging to a text file, then the effect will be the same either way, and it is best to leave the setting on, since most syslog implementations either cannot handle large messages or would need to be specially configured to handle them. But if syslog is ultimately writing into some other medium, it might be necessary or more useful to keep messages logically together.
  +
  This parameter can only be set in the `+postgresql.conf+` file or on the server command line.
[.term]#`+event_source+` (`+string+`) ::
  When logging to event log is enabled, this parameter determines the program name used to identify PostgreSQL messages in the log. The default is `+PostgreSQL+`. This parameter can only be set in the `+postgresql.conf+` file or on the server command line.

+

+
[TIP]
====
==== Tip

If you set a nonempty value for `+log_line_prefix+`, you should usually make its last character be a space, to provide visual separation from the rest of the log line. A punctuation character can be used too.
====
+
[TIP]
====
==== Tip

Syslog produces its own time stamp and process ID information, so you probably do not want to include those escapes if you are logging to syslog.
====
+
[TIP]
====
==== Tip

The `+%q+` escape is useful when including information that is only available in session (backend) context like user or database name. For example:

  ====
[.term]#`+log_lock_waits+` (`+boolean+`) ::
  Controls whether a log message is produced when a session waits longer than link:runtime-config-locks.html#GUC-DEADLOCK-TIMEOUT[deadlock_timeout] to acquire a lock. This is useful in determining if lock waits are causing poor performance. The default is `+off+`. Only superusers can change this setting.
[.term]#`+log_statement+` (`+enum+`) ::
  Controls which SQL statements are logged. Valid values are `+none+` (off), `+ddl+`, `+mod+`, and `+all+` (all statements). `+ddl+` logs all data definition statements, such as `+CREATE+`, `+ALTER+`, and `+DROP+` statements. `+mod+` logs all `+ddl+` statements, plus data-modifying statements such as `+INSERT+`, `+UPDATE+`, `+DELETE+`, `+TRUNCATE+`, and `+COPY FROM+`. `+PREPARE+`, `+EXECUTE+`, and `+EXPLAIN ANALYZE+` statements are also logged if their contained command is of an appropriate type. For clients using extended query protocol, logging occurs when an Execute message is received, and values of the Bind parameters are included (with any embedded single-quote marks doubled).
  +
  The default is `+none+`. Only superusers can change this setting.
  +
  [NOTE]
  ====
  ==== Note

Statements that contain simple syntax errors are not logged even by the `+log_statement+` = `+all+` setting, because the log message is emitted only after basic parsing has been done to determine the statement type. In the case of extended query protocol, this setting likewise does not log statements that fail before the Execute phase (i.e., during parse analysis or planning). Set `+log_min_error_statement+` to `+ERROR+` (or lower) to log such statements.

  Logged statements might reveal sensitive data and even contain plaintext passwords.
  ====
[.term]#`+log_replication_commands+` (`+boolean+`) ::
  Causes each replication command to be logged in the server log. See link:protocol-replication.html[Section 53.4] for more information about replication command. The default value is `+off+`. Only superusers can change this setting.
[.term]#`+log_temp_files+` (`+integer+`) ::
  Controls logging of temporary file names and sizes. Temporary files can be created for sorts, hashes, and temporary query results. A log entry is made for each temporary file when it is deleted. A value of zero logs all temporary file information, while positive values log only files whose size is greater than or equal to the specified number of kilobytes. The default setting is -1, which disables such logging. Only superusers can change this setting.
[.term]#`+log_timezone+` (`+string+`) ::
  Sets the time zone used for timestamps written in the server log. Unlike link:runtime-config-client.html#GUC-TIMEZONE[TimeZone], this value is cluster-wide, so that all sessions will report timestamps consistently. The built-in default is `+GMT+`, but that is typically overridden in `+postgresql.conf+`; initdb will install a setting there corresponding to its system environment. See link:datatype-datetime.html#DATATYPE-TIMEZONES[Section 8.5.3] for more information. This parameter can only be set in the `+postgresql.conf+` file or on the server command line.