pgpool-II 4.7.0 Documentation
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# 5.7. Error Reporting and Logging

## 5.7.1. Where To Log

`log_destination` (`string`)

  Pgpool-II supports two destinations for logging the Pgpool-II messages. The supported log destinations are `stderr` and `syslog`. You can also set this parameter to a list of desired log destinations separated by commas if you want the log messages on the multiple destinations.

             #for example to log on both syslog and stderr
             log_destination = 'syslog,stderr'

  The default is to log to `stderr` only.

  > Note: On some systems you will need to alter the configuration of your system's syslog daemon in order to make use of the `syslog` option for `log_destination`. Pgpool-II can log to syslog facilities LOCAL0 through LOCAL7 (see syslog_facility), but the default syslog configuration on most platforms will discard all such messages. You will need to add something like:

  >     	 local0.*    /var/log/pgpool.log

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

  This parameter can be changed by reloading the Pgpool-II configurations.

`logging_collector` (`boolean`)

  This parameter enables the logging collector, which is a background process that captures log messages sent to stderr and redirects them into log files.

  > Note: It is possible to log to stderr without using the logging collector; the log messages will just go to wherever the server's stderr is directed. However, that method is only suitable for low log volumes, since it provides no convenient way to rotate log files.

  This parameter can only be set at the Pgpool-II start.

  `logging_collector` is not available prior to Pgpool-II V4.2.

`log_directory` (`string`)

  When logging_collector is enabled, this parameter determines the directory in which log files will be created.

  The default is `/tmp/pgpool_logs`.

  This parameter can be changed by reloading the Pgpool-II configurations.

`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. The supported %-escapes are similar to those listed in the Open Group's strftimespecification.

  If you specify a file name without escapes, you should plan to use a log rotation utility to avoid eventually filling the entire disk.

  The default is `pgpool-%Y-%m-%d_%H%M%S.log`.

  This parameter can be changed by reloading the Pgpool-II configurations.

`log_file_mode` (`integer`)

  This parameter sets the permissions for log files when logging_collector is enabled. The parameter value is expected to be a numeric mode specified in the format accepted by the `chmod` and `umask` system calls.

  > Note: To use the customary octal format the number must start with a 0 (zero).

  This parameter can be changed by reloading the Pgpool-II configurations.

`log_rotation_age` (`integer`)

  When logging_collector is enabled, this parameter determines the maximum amount of time to use an individual log file, after which a new log file will be created. If this value is specified without units, it is taken as minutes. The default is 24 hours.

  Set to zero to disable time-based creation of new log files.

  This parameter can be changed by reloading the Pgpool-II configurations.

`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 be changed by reloading the Pgpool-II configurations.

`log_truncate_on_rotation` (`boolean`)

  When logging_collector is enabled, this parameter will cause Pgpool-II 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 the 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 pgpool-%H.log would result in generating twenty-four hourly log files and then cyclically overwriting them.

  This parameter can be changed by reloading the Pgpool-II configurations.

`syslog_facility` (`enum`)

  See also the documentation of your system's syslog daemon. When logging to syslog is enabled, this parameter determines the syslog `"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 be changed by reloading the Pgpool-II configurations.

`syslog_ident` (`string`)

  When logging to syslog is enabled, this parameter determines the program name used to identify Pgpool-II messages in syslog logs. The default is `pgpool`.

  This parameter can be changed by reloading the Pgpool-II configurations.

## 5.7.2. When To Log

`client_min_messages` (`enum`)

  Controls which minimum message levels are sent to the client. Valid values are `DEBUG5`, `DEBUG4`, `DEBUG3`, `DEBUG2`, `DEBUG1`, `LOG`, `NOTICE`, `WARNING` and `ERROR`. Each level includes all the levels that follow it. The default is `NOTICE`.

  This parameter can be changed by reloading the Pgpool-II configurations. You can also use PGPOOL SET command to alter the value of this parameter for a current session.

`log_min_messages` (`enum`)

  The default is WARNING. Controls which minimum message levels are emitted to log. Valid values are `DEBUG5`, `DEBUG4`, `DEBUG3`, `DEBUG2`, `DEBUG1`, `INFO`, `NOTICE`, `WARNING`, `ERROR`, `LOG`, `FATAL`, and `PANIC`. Each level includes all the levels that follow it. The default is `WARNING`.

  This parameter can be changed by reloading the Pgpool-II configurations. You can also use PGPOOL SET command to alter the value of this parameter for a current session.

## 5.7.3. What To Log

`log_statement` (`boolean`)

  Setting to on, prints all SQL statements to the log.

  This parameter can be changed by reloading the Pgpool-II configurations. You can also use PGPOOL SET command to alter the value of this parameter for a current session.

`log_per_node_statement` (`boolean`)

  Similar to log_statement, except that it print the logs for each DB node separately. It can be useful to make sure that replication or load-balancing is working.

  This parameter can be changed by reloading the Pgpool-II configurations. You can also use PGPOOL SET command to alter the value of this parameter for a current session.

`notice_per_node_statement` (`boolean`)

  Similar to log_per_node_statement, except that it prints the statement logs for each DB node separately as a NOTICE message. With the default client_min_messages setting (that is NOTICE), the log message will be printed on client's terminal as well. This is convenient for clients because it does not need to access Pgpool-II log file. Note that unlike log_per_node_statement, notice_per_node_statement does not print internal queries, (e.g., system catalog inquiry). This is because this feature is designed to be used for testing as well. As internal queries tend to be non-deterministic, printing them in testing is not helpful. For the same reason, backend process id is not printed.

  This parameter can be changed by reloading the Pgpool-II configurations. You can also use PGPOOL SET command to alter the value of this parameter for a current session.

`log_client_messages` (`boolean`)

  Setting to on, prints client messages to the log.

  This parameter can be changed by reloading the Pgpool-II configurations. You can also use PGPOOL SET command to alter the value of this parameter for a current session.

`log_backend_messages` (`enum`)

  Setting to `terse` or `verbose`, prints backend messages to the log. With `terse` the number of same kind of messages are recorded and is printed when different kind of messages is sent. Below is an example.

             LOG:  last DataRow message from backend 0 repeated 10 times

  Thus the log will not be printed if the process corresponding to the session is killed. If you want to print the log even in this case, use `verbose` option. Note that with the option each repeated message is printed and lots of log lines are printed. The default is `none`, which disables printing log messages from backend.

  This parameter can be changed by reloading the Pgpool-II configurations. You can also use PGPOOL SET command to alter the value of this parameter for a current session.

`log_hostname` (`boolean`)

  Setting to on, prints the hostname instead of IP address in the `ps` command result, and connection logs (when log_connections is on).

  This parameter can be changed by reloading the Pgpool-II configurations.

`log_connections` (`boolean`)

  Setting to on, prints all client connections from to the log.

  This parameter can be changed by reloading the Pgpool-II configurations.

`log_disconnections` (`boolean`)

  Setting to on, prints all client connection terminations to the log.

  This parameter can be changed by reloading the Pgpool-II configurations.

`log_pcp_processes` (`boolean`)

  Setting to on, enable logging about normal PCP Process fork and exit status. Default is off.

  This parameter can be changed by reloading the Pgpool-II configurations.

`log_error_verbosity` (`enum`)

  Controls the amount of detail emitted for each message that is logged. Valid values are `TERSE`, `DEFAULT`, and `VERBOSE`, each adding more fields to displayed messages. `TERSE` excludes the logging of `DETAIL`, `HINT`, `QUERY` and `CONTEXT` error information.

  This parameter can be changed by reloading the Pgpool-II configurations. You can also use PGPOOL SET command to alter the value of this parameter for a current session.

`log_line_prefix` (`string`)

  This is a `printf`-style string that is output at the beginning of each log line. `%` characters begin "escape sequences" that are replaced with information outlined below. All unrecognized escapes are ignored. Other characters are copied straight to the log line. Default is '%m: %a pid %p: ', which prints timestamp, application name and process id.

  Table 5-6. log_line_prefix escape options

  Escape | Effect
  --- | ---
  %a | Application name. The initial value for child (session process) is "child". If Clients set application name (either in the startup message or by using SET command), application name will be changed accordingly. In other types of process, application name is a hard coded string. see Table 5-7.
  %p | Process ID (PID)
  %P | Process name
  %t | Time stamp without milliseconds
  %m | Time stamp with milliseconds
  %d | Database name
  %u | User name
  %l | Log line number for each process
  %% | '%' character

  Table 5-7. application names in various process

  Process type | application name
  --- | ---
  main | main
  child | child
  streaming replication delay check worker | sr_check_worker
  watchdog heart beat sender | heart_beat_sender
  watchdog heart beat receiver | heart_beat_receiver
  watchdog | watchdog
  watchdog life check | life_check
  follow primary child | follow_child
  watchdog utility | watchdog_utility
  pcp main | pcp_main
  pcp child | pcp_child
  health check process | health_check%d (%d is replaced with backend node id)
  logger process | logger (Note that the application name "logger" will not be output to the log file managed by logger process)

  This parameter can be changed by reloading the Pgpool-II configurations.

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