18.8. Error Reporting and Logging
18.8.1. Where To Log
log_destination
(string
)Postgres Pro 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.When either stderr or csvlog are included, the file
current_logfiles
is created to record the location of the log file(s) currently in use by the logging collector and the associated logging destination. This provides a convenient way to find the logs currently in use by the instance. Here is an example of this file's content:stderr log/postgresql.log csvlog log/postgresql.csv
current_logfiles
is recreated when a new log file is created as an effect of rotation, and whenlog_destination
is reloaded. It is removed when neither stderr nor csvlog are included inlog_destination
, and when the logging collector is disabled.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
. Postgres Pro can log to syslog facilitiesLOCAL0
throughLOCAL7
(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.
On Windows, when you use the
eventlog
option forlog_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 Section 17.11 for details.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 thepostgresql.conf
file or on the server command line. The default islog
.log_filename
(string
)When
logging_collector
is enabled, this parameter sets the file names of the created log files. The value is treated as astrftime
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'sstrftime
is not used directly, so platform-specific (nonstandard) extensions do not work. The default ispostgresql-%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. (Iflog_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 thechmod
andumask
system calls. (To use the customary octal format the number must start with a0
(zero).)The default permissions are
0600
, meaning only the server owner can read or write the log files. The other commonly useful setting is0640
, 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 thepostgresql.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 thepostgresql.conf
file or on the server command line.log_truncate_on_rotation
(boolean
)When
logging_collector
is enabled, this parameter will cause Postgres Pro 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 alog_filename
likepostgresql-%H.log
would result in generating twenty-four hourly log files and then cyclically overwriting them. This parameter can only be set in thepostgresql.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, setlog_filename
toserver_log.%a
,log_truncate_on_rotation
toon
, andlog_rotation_age
to1440
.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
toserver_log.%H%M
,log_truncate_on_rotation
toon
,log_rotation_age
to60
, andlog_rotation_size
to1000000
. Including%M
inlog_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 isLOCAL0
. See also the documentation of your system's syslog daemon. This parameter can only be set in thepostgresql.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 Postgres Pro messages in syslog logs. The default is
postgres
. This parameter can only be set in thepostgresql.conf
file or on the server command line.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 “--- 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.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, Postgres Pro 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.event_source
(string
)When logging to event log is enabled, this parameter determines the program name used to identify Postgres Pro messages in the log. The default is
Postgres Pro
. This parameter can only be set in thepostgresql.conf
file or on the server command line.
18.8.2. When To Log
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
, andPANIC
. Each level includes all the levels that follow it. The later the level, the fewer messages are sent to the log. The default isWARNING
. Note thatLOG
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
, andPANIC
. The default isERROR
, 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 toPANIC
. 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 18.2 explains the message severity levels used by Postgres Pro. If logging output is sent to syslog or Windows' eventlog, the severity levels are translated as shown in the table.
Table 18.2. 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. | CRIT | ERROR |
18.8.3. What To Log
Note
What you choose to log can have security implications; see Section 23.3.
application_name
(string
)The
application_name
can be any string of less thanNAMEDATALEN
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 thepg_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 theapplication_name
value. Other characters will be replaced with question marks (?
).debug_print_parse
(boolean
)debug_print_rewritten
(boolean
)debug_print_plan
(boolean
)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 bydebug_print_parse
,debug_print_rewritten
, ordebug_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. Only superusers can change this parameter at session start, and it cannot be changed at all within a session. 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
)Causes session terminations to be logged. The log output provides information similar to
log_connections
, plus the duration of the session. Only superusers can change this parameter at session start, and it cannot be changed at all within a session. The default isoff
.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, iflog_duration
ison
andlog_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
, andVERBOSE
, each adding more fields to displayed messages.TERSE
excludes the logging ofDETAIL
,HINT
,QUERY
, andCONTEXT
error information.VERBOSE
output includes theSQLSTATE
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 will be treated as empty by background processes such as the main server process. Status information may be aligned either left or right by specifying a numeric literal after the % and before the option. A negative value will cause the status information to be padded on the right with spaces to give it a minimum width, whereas a positive value will pad on the left. Padding can be useful to aid human readability in log files. This parameter can only be set in thepostgresql.conf
file or on the server command line. The default is'%m [%p] '
which logs a time stamp and the process ID.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 %n
Time stamp with milliseconds (as a Unix epoch) 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 frompg_stat_activity
, use this query:SELECT to_hex(trunc(EXTRACT(EPOCH FROM backend_start))::integer) || '.' || to_hex(pid) 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.
Tip
The
%q
escape is useful when including information that is only available in session (backend) context like user or database name. For example:log_line_prefix = '%m [%p] %q%u@%d/%a '
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
. Only superusers can change this setting.log_statement
(enum
)Controls which SQL statements are logged. Valid values are
none
(off),ddl
,mod
, andall
(all statements).ddl
logs all data definition statements, such asCREATE
,ALTER
, andDROP
statements.mod
logs allddl
statements, plus data-modifying statements such asINSERT
,UPDATE
,DELETE
,TRUNCATE
, andCOPY FROM
.PREPARE
,EXECUTE
, andEXPLAIN 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). Setlog_min_error_statement
toERROR
(or lower) to log such statements.Logged statements might reveal sensitive data and even contain plaintext passwords.
log_replication_commands
(boolean
)Causes each replication command to be logged in the server log. See Section 51.4 for more information about replication command. The default value is
off
. Only superusers can change this setting.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. The built-in default is
GMT
, but that is typically overridden inpostgresql.conf
; initdb will install a setting there corresponding to its system environment. See Section 8.5.3 for more information. This parameter can only be set in thepostgresql.conf
file or on the server command line.
18.8.4. Using CSV-Format Log Output
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 Postgres Pro 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:
CREATE TABLE postgres_log ( log_time timestamp(3) with time zone, user_name text, database_name text, process_id integer, connection_from text, session_id text, session_line_num bigint, command_tag text, session_start_time timestamp with time zone, virtual_transaction_id text, transaction_id bigint, error_severity text, sql_state_code text, message text, detail text, hint text, internal_query text, internal_query_pos integer, context text, query text, query_pos integer, location text, application_name text, PRIMARY KEY (session_id, session_line_num) );
To import a log file into this table, use the COPY FROM
command:
COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
It is also possible to access the file as a foreign table, using the supplied file_fdw module.
There are a few things you need to do to simplify importing CSV log files:
Set
log_filename
andlog_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
toon
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 causeCOPY
to fail.
18.8.5. Process Title
These settings control how process titles of server processes are modified. Process titles are typically viewed using programs like ps or, on Windows, Process Explorer. See Section 27.1 for details.
cluster_name
(string
)Sets the cluster name that appears in the process title for all server processes in this cluster. The name can be any string of less than
NAMEDATALEN
characters (64 characters in a standard build). Only printable ASCII characters may be used in thecluster_name
value. Other characters will be replaced with question marks (?
). No name is shown if this parameter is set to the empty string''
(which is the default). This parameter can only be set at server start.update_process_title
(boolean
)Enables updating of the process title every time a new SQL command is received by the server. This setting defaults to
on
on most platforms, but it defaults tooff
on Windows due to that platform's larger overhead for updating the process title. Only superusers can change this setting.