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17.7. Error Reporting and Logging

17.7.1. Where To Log

log_destination (string)

PostgreSQL supports several methods for logging server messages, including stderr and syslog. On Windows, eventlog is also supported. Set this parameter to a list of desired log destinations separated by commas. The default is to log to stderr only. This parameter can only be set in the postgresql.conf file or on the server command line.

redirect_stderr (boolean)

This parameter allows messages sent to stderr to be captured and redirected into log files. This method, in combination with logging to stderr, is often more useful than logging to syslog, since some types of messages may not appear in syslog output (a common example is dynamic-linker failure messages). This parameter can only be set at server start.

log_directory (string)

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

log_filename (string)

When redirect_stderr 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. If no %-escapes are present, PostgreSQL will append the epoch of the new log file's open time. For example, if log_filename were server_log, then the chosen file name would be server_log.1093827753 for a log starting at Sun Aug 29 19:02:33 2004 MST. This parameter can only be set in the postgresql.conf file or on the server command line.

log_rotation_age (integer)

When redirect_stderr 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.

log_rotation_size (integer)

When redirect_stderr 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.

log_truncate_on_rotation (boolean)

When redirect_stderr 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 may occur to select a file name different from the hour's initial file name.

syslog_facility (string)

When logging to syslog is enabled, this parameter determines the syslog "facility" to be used. You may 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. This parameter is unavailable unless the server is compiled with support for syslog.

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. This parameter is unavailable unless the server is compiled with support for syslog.

17.7.2. When To Log

client_min_messages (string)

Controls which message levels are sent to the client. Valid values are DEBUG5, DEBUG4, DEBUG3, DEBUG2, DEBUG1, LOG, NOTICE, WARNING, ERROR, FATAL, and PANIC. Each level includes all the levels that follow it. The later the level, the fewer messages are sent. The default is NOTICE. Note that LOG has a different rank here than in log_min_messages.

log_min_messages (string)

Controls which message levels are written to the server 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 later the level, the fewer messages are sent to the log. The default is NOTICE. Note that LOG has a different rank here than in client_min_messages. Only superusers can change this setting.

log_error_verbosity (string)

Controls the amount of detail written in the server log for each message that is logged. Valid values are TERSE, DEFAULT, and VERBOSE, each adding more fields to displayed messages. Only superusers can change this setting.

log_min_error_statement (string)

Controls whether or not the SQL statement that causes an error condition will be recorded in the server log. The current SQL statement is included in the log entry for any message of the specified severity or higher. Valid values are DEBUG5, DEBUG4, DEBUG3, DEBUG2, DEBUG1, INFO, NOTICE, WARNING, ERROR, FATAL, and PANIC. The default is ERROR, which means statements causing errors, fatal errors, or panics will be logged. To effectively turn off logging of failing statements, set this parameter to PANIC. Only superusers can change this setting.

log_min_duration_statement (integer)

Causes the duration of each completed statement to be logged if the statement ran for at least the specified number of milliseconds. Setting this to zero prints all statement durations. Minus-one (the default) disables logging statement durations. For example, if you set it to 250ms then all SQL statements that run 250ms or longer will be logged. Enabling this parameter can be helpful in tracking down unoptimized queries in your applications. Only superusers can change this setting.

For clients using extended query protocol, durations of the Parse, Bind, and Execute steps are logged independently.

Note: When using this option together with log_statement, the text of statements that are logged because of log_statement will not be repeated in the duration log message. If you are not using syslog, it is recommended that you log the PID or session ID using log_line_prefix so that you can link the statement message to the later duration message using the process ID or session ID.

silent_mode (boolean)

Runs the server silently. If this parameter is set, the server will automatically run in background and any controlling terminals are disassociated. The server's standard output and standard error are redirected to /dev/null, so any messages sent to them will be lost. Unless syslog logging is selected or redirect_stderr is enabled, using this parameter is discouraged because it makes it impossible to see error messages. This parameter can only be set at server start.

Here is a list of the various message severity levels used in these settings:

DEBUG[1-5]

Provides information for use by developers.

INFO

Provides information implicitly requested by the user, e.g., during VACUUM VERBOSE.

NOTICE

Provides information that may be helpful to users, e.g., truncation of long identifiers and the creation of indexes as part of primary keys.

WARNING

Provides warnings to the user, e.g., COMMIT outside a transaction block.

ERROR

Reports an error that caused the current command to abort.

LOG

Reports information of interest to administrators, e.g., checkpoint activity.

FATAL

Reports an error that caused the current session to abort.

PANIC

Reports an error that caused all sessions to abort.

17.7.3. What To Log

debug_print_parse (boolean)
debug_print_rewritten (boolean)
debug_print_plan (boolean)
debug_pretty_print (boolean)

These parameters enable various debugging output to be emitted. For each executed query, they print the resulting parse tree, the query rewriter output, or the execution plan. debug_pretty_print indents these displays to produce a more readable but much longer output format. client_min_messages or log_min_messages must be DEBUG1 or lower to actually send this output to the client or the server log, respectively. These parameters are off by default.

log_connections (boolean)

This outputs a line to the server log detailing each successful connection. This is off by default, although it is probably very useful. Some client programs, like psql, attempt to connect twice while determining if a password is required, so duplicate "connection received" messages do not necessarily indicate a problem. This parameter can only be set in the postgresql.conf file or on the server command line.

log_disconnections (boolean)

This outputs a line in the server log similar to log_connections but at session termination, and includes the duration of the session. This is off by default. This parameter can only be set in the postgresql.conf file or on the server command line.

log_duration (boolean)

Causes the duration of every completed statement to be logged. The default is off. Only superusers can change this setting.

For clients using extended query protocol, durations of the Parse, Bind, and Execute steps are logged independently.

Note: The difference between setting this option and setting log_min_duration_statement to zero is that exceeding log_min_duration_statement forces the text of the query to be logged, but this option doesn't. Thus, if log_duration is on and log_min_duration_statement has a positive value, all durations are logged but the query text is included only for statements exceeding the threshold. This behavior can be useful for gathering statistics in high-load installations.

log_line_prefix (string)

This is a printf-style string that is output at the beginning of each log line. The default is an empty string. Each recognized escape is replaced as outlined below - anything else that looks like an escape is ignored. Other characters are copied straight to the log line. Some escapes are only recognized by session processes, and do not apply to background processes such as the main server process. Syslog produces its own time stamp and process ID information, so you probably do not want to use those escapes if you are using syslog. This parameter can only be set in the postgresql.conf file or on the server command line.

Escape Effect Session only
%u User name yes
%d Database name yes
%r Remote host name or IP address, and remote port yes
%h Remote host name or IP address yes
%p Process ID no
%t Time stamp (no milliseconds, no timezone on Windows) no
%m Time stamp with milliseconds no
%i Command tag: This is the command that generated the log line. yes
%c Session ID: A unique identifier for each session. It is 2 4-byte hexadecimal numbers (without leading zeros) separated by a dot. The numbers are the session start time and the process ID, so this can also be used as a space saving way of printing these items. yes
%l Number of the log line for each process, starting at 1 no
%s Session start time stamp yes
%x Transaction ID yes
%q Does not produce any output, but tells non-session processes to stop at this point in the string. Ignored by session processes. no
%% Literal % no
log_statement (string)

Controls which SQL statements are logged. Valid values are none, ddl, mod, and all. 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: 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.

log_hostname (boolean)

By default, connection log messages only show the IP address of the connecting host. Turning on this parameter causes logging of the host name as well. Note that depending on your host name resolution setup this might impose a non-negligible performance penalty. This parameter can only be set in the postgresql.conf file or on the server command line.

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