PostgreSQL supports several methods
for logging server messages, including
stderr, csvlog 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.
If csvlog is included in log_destination,
log entries are output in "comma separated
value" (CSV) format, which is convenient for
loading logs into programs.
See Section 18.8.4 for details.
logging_collector must be enabled to generate
CSV-format log output.
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 syslog option for
log_destination. PostgreSQL
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/postgresql
to the syslog daemon's configuration file
to make it work.
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.
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: 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. 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: 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.
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 pg_log.
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 log_timezone.)
The supported %-escapes are similar to those
listed in the Open Group's 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.
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 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.
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.
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.
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.
syslog_facility (enum)
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 only be set in the postgresql.conf
file or on the server command line.
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.
silent_mode (boolean)
Runs the server silently. If this parameter is set, the server
will automatically run in background and disassociate from the
controlling terminal.
This parameter can only be set at server start.
Caution
When this parameter is set,
the server's standard output and standard error are redirected
to the file postmaster.log within the data directory.
There is no provision for rotating this file, so it will grow
indefinitely unless server log output is redirected elsewhere
by other settings. It is recommended that log_destination
be set to syslog or that logging_collector be
enabled when using this option. Even with those measures, errors
reported early during startup may appear in
postmaster.log rather than the normal log destination.
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 (enum)
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 WARNING. Note that
LOG has a different rank here than in
client_min_messages.
Only superusers can change this setting.
log_min_error_statement (enum)
Controls which SQL statements that cause an error
condition are 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,
LOG,
FATAL, and PANIC.
The default is ERROR, which means statements
causing errors, log messages, 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.
Table 18-1 explains the message
severity levels used by PostgreSQL. If logging output
is sent to syslog or Windows'
eventlog, the severity levels are translated
as shown in the table.
Table 18-1. Message Severity Levels
Severity
Usage
syslog
eventlog
DEBUG1..DEBUG5
Provides successively-more-detailed information for use by
developers.
DEBUG
INFORMATION
INFO
Provides information implicitly requested by the user,
e.g., output from VACUUM VERBOSE.
INFO
INFORMATION
NOTICE
Provides information that might be helpful to users, e.g.,
notice of truncation of long identifiers.
NOTICE
INFORMATION
WARNING
Provides warnings of likely problems, e.g., COMMIT
outside a transaction block.
NOTICE
WARNING
ERROR
Reports an error that caused the current command to
abort.
WARNING
ERROR
LOG
Reports information of interest to administrators, e.g.,
checkpoint activity.
INFO
INFORMATION
FATAL
Reports an error that caused the current session to
abort.
ERR
ERROR
PANIC
Reports an error that caused all database sessions to abort.
The application_name can be any string of less than
NAMEDATALEN characters (64 characters in a standard build).
It is typically set by an application upon connection to the server.
The name will be displayed in the pg_stat_activity view
and included in CSV log entries. It can also be included in regular
log entries via the log_line_prefix parameter.
Only printable ASCII characters may be used in the
application_name value. Other characters will be
replaced with question marks (?).
These parameters enable various debugging output to be emitted.
When set, they print the resulting parse tree, the query rewriter
output, or the execution plan for each executed query.
These messages are emitted at LOG message level, so by
default they will appear in the server log but will not be sent to the
client. You can change that by adjusting
client_min_messages and/or
log_min_messages.
These parameters are off by default.
debug_pretty_print (boolean)
When set, debug_pretty_print indents the messages
produced by debug_print_parse,
debug_print_rewritten, or
debug_print_plan. This results in more readable
but much longer output than the "compact" format used when
it is off. It is on by default.
log_checkpoints (boolean)
Causes checkpoints and restartpoints to be logged in the server log.
Some statistics are included in the log messages, including the number
of buffers written and the time spent writing them.
This parameter can only be set in the postgresql.conf
file or on the server command line. The default is off.
log_connections (boolean)
Causes each attempted connection to the server to be logged,
as well as successful completion of client authentication.
This parameter cannot be changed after session start.
The default is off.
Note: 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.
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 cannot be changed after session start.
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_error_verbosity (enum)
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. TERSE excludes
the logging of DETAIL, HINT,
QUERY, and CONTEXT error information.
VERBOSE output includes the SQLSTATE error
code (see also Appendix A) and the source code file name, function name,
and line number that generated the error.
Only superusers can change this setting.
log_hostname (boolean)
By default, connection log messages only show the IP address of the
connecting host. Turning this parameter on 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.
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 status information as outlined below.
Unrecognized escapes are ignored. Other
characters are copied straight to the log line. Some escapes are
only recognized by session processes, and are ignored by
background processes such as the main server process.
This parameter can only be set in the postgresql.conf
file or on the server command line. The default is an empty string.
Escape
Effect
Session only
%a
Application name
yes
%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 without milliseconds
no
%m
Time stamp with milliseconds
no
%i
Command tag: type of session's current command
yes
%e
SQLSTATE error code
no
%c
Session ID: see below
no
%l
Number of the log line for each session or process, starting at 1
no
%s
Process start time stamp
no
%v
Virtual transaction ID (backendID/localXID)
no
%x
Transaction ID (0 if none is assigned)
no
%q
Produces no output, but tells non-session
processes to stop at this point in the string; ignored by
session processes
no
%%
Literal %
no
The %c escape prints a quasi-unique session identifier,
consisting of two 4-byte hexadecimal numbers (without leading zeros)
separated by a dot. The numbers are the process start time and the
process ID, so %c can also be used as a space saving way
of printing those items. For example, to generate the session
identifier from pg_stat_activity, use this query:
SELECT to_hex(EXTRACT(EPOCH FROM backend_start)::integer) || '.' ||
to_hex(procpid)
FROM pg_stat_activity;
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: 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.
log_lock_waits (boolean)
Controls whether a log message is produced when a session waits
longer than deadlock_timeout to acquire a
lock. This is useful in determining if lock waits are causing
poor performance. The default is off.
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: 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_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.
log_timezone (string)
Sets the time zone used for timestamps written in the server log.
Unlike timezone, this value is cluster-wide,
so that all sessions will report timestamps consistently.
If not explicitly set, the server initializes this variable to the
time zone specified by its system environment. See Section 8.5.3 for more information.
This parameter can only be set in the postgresql.conf
file or on the server command line.
Including csvlog in the log_destination list
provides a convenient way to import log files into a database table.
This option emits log lines in comma-separated-values
(CSV) format,
with these columns:
time stamp with milliseconds,
user name,
database name,
process ID,
client host:port number,
session ID,
per-session line number,
command tag,
session start time,
virtual transaction ID,
regular transaction ID,
error severity,
SQLSTATE code,
error message,
error message detail,
hint,
internal query that led to the error (if any),
character count of the error position therein,
error context,
user query that led to the error (if any and enabled by
log_min_error_statement),
character count of the error position therein,
location of the error in the PostgreSQL source code
(if log_error_verbosity is set to verbose),
and application name.
Here is a sample table definition for storing CSV-format log output:
To import a log file into this table, use the COPY FROM
command:
COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
There are a few things you need to do to simplify importing CSV log
files:
Set log_filename and
log_rotation_age to provide a consistent,
predictable naming scheme for your log files. This lets you
predict what the file name will be and know when an individual log
file is complete and therefore ready to be imported.
Set log_rotation_size to 0 to disable
size-based log rotation, as it makes the log file name difficult
to predict.
Set log_truncate_on_rotation to on so
that old log data isn't mixed with the new in the same file.
The table definition above includes a primary key specification.
This is useful to protect against accidentally importing the same
information twice. The COPY command commits all of the
data it imports at one time, so any error will cause the entire
import to fail. If you import a partial log file and later import
the file again when it is complete, the primary key violation will
cause the import to fail. Wait until the log is complete and
closed before importing. This procedure will also protect against
accidentally importing a partial line that hasn't been completely
written, which would also cause COPY to fail.