log_destination (string)
LightDB supports several methods
for logging server messages, including
stderr, csvlog and
syslog. 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 lightdb.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/lightdb.log csvlog log/lightdb.csv
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 stderr
nor csvlog are included
in log_destination, and when the logging collector is
disabled.
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. LightDB
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/lightdb
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.
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.
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 lightdb.conf
file or on the server command line.
The default is 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 lightdb-%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.
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 lightdb.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.
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 lightdb.conf
file or on the server command line.
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 only be set in the lightdb.conf
file or on the server command line.
lightdb_log_retention_age (integer)
When logging_collector is enabled,
This parameter determines the maximum time to keep the log file,
the log longer than this time will be cleaned up when switching the log file.
If this value is specified without units, it is taken as minutes.
The default is 0.
Set to zero to disable time-based delete of log files.
This parameter can only be set in the lightdb.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 amount of data has been emitted into a log file,
a new log file will be created.
If this value is specified without units, it is taken as kilobytes.
The default is 10 megabytes.
Set to zero to disable size-based creation of new log files.
This parameter can only be set in the lightdb.conf
file or on the server command line.
log_truncate_on_rotation (boolean)
When logging_collector is enabled,
this parameter will cause LightDB 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 lightdb-%H.log
would result in generating twenty-four hourly log files and then
cyclically overwriting them.
This parameter can only be set in the lightdb.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 lightdb.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
LightDB messages in
syslog logs. The default is
lightdb.
This parameter can only be set in the lightdb.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 lightdb.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, LightDB 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 lightdb.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
LightDB messages in
the log. The default is LightDB.
This parameter can only be set in the lightdb.conf
file or on the server command line.
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 amount of time.
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.
If this value is specified without units, it is taken as milliseconds.
Setting this to zero prints all statement durations.
-1 (the default) disables logging statement
durations. Only superusers can change this setting.
This overrides log_min_duration_sample, meaning that queries with duration exceeding this setting are not subject to sampling and are always logged.
For clients using extended query protocol, durations of the Parse, Bind, and Execute steps are logged independently.
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.
log_min_duration_sample (integer)
Allows sampling the duration of completed statements that ran for
at least the specified amount of time. This produces the same
kind of log entries as
log_min_duration_statement, but only for a
subset of the executed statements, with sample rate controlled by
log_statement_sample_rate.
For example, if you set it to 100ms then all
SQL statements that run 100ms or longer will be considered for
sampling. Enabling this parameter can be helpful when the
traffic is too high to log all queries.
If this value is specified without units, it is taken as milliseconds.
Setting this to zero samples all statement durations.
-1 (the default) disables sampling statement
durations. Only superusers can change this setting.
This setting has lower priority
than log_min_duration_statement, meaning that
statements with durations
exceeding log_min_duration_statement are not
subject to sampling and are always logged.
Other notes for log_min_duration_statement
apply also to this setting.
log_statement_sample_rate (floating point)
Determines the fraction of statements with duration exceeding
log_min_duration_sample that will be logged.
Sampling is stochastic, for example 0.5 means
there is statistically one chance in two that any given statement
will be logged.
The default is 1.0, meaning to log all sampled
statements.
Setting this to zero disables sampled statement-duration logging,
the same as setting
log_min_duration_sample to
-1.
Only superusers can change this setting.
log_transaction_sample_rate (floating point)
Sets the fraction of transactions whose statements are all logged,
in addition to statements logged for other reasons. It applies to
each new transaction regardless of its statements' durations.
Sampling is stochastic, for example 0.1 means
there is statistically one chance in ten that any given transaction
will be logged.
log_transaction_sample_rate can be helpful to
construct a sample of transactions.
The default is 0, meaning not to log
statements from any additional transactions. Setting this
to 1 logs all statements of all transactions.
Only superusers can change this setting.
Like all statement-logging options, this option can add significant overhead.
Table 18.2 explains the message severity levels used by LightDB. If logging output is sent to syslog, 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 |
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 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 (?).
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 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 lightdb.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.
Some client programs, like ltsql, 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 is off.
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.
The difference between enabling log_duration 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 lightdb.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 the lightdb.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 |
%b | Backend type | no |
%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 backend type corresponds to the column
backend_type in the view
pg_stat_activity,
but additional types can appear
in the log that don't show in that view.
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(trunc(EXTRACT(EPOCH FROM backend_start))::integer) || '.' ||
to_hex(pid)
FROM pg_stat_activity;
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.
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.
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_parameter_max_length (integer)
If greater than zero, each bind parameter value logged with a
non-error statement-logging message is trimmed to this many bytes.
Zero disables logging of bind parameters for non-error statement logs.
-1 (the default) allows bind parameters to be
logged in full.
If this value is specified without units, it is taken as bytes.
Only superusers can change this setting.
This setting only affects log messages printed as a result of log_statement, log_duration, and related settings. Non-zero values of this setting add some overhead, particularly if parameters are sent in binary form, since then conversion to text is required.
log_parameter_max_length_on_error (integer)
If greater than zero, each bind parameter value reported in error
messages is trimmed to this many bytes.
Zero (the default) disables including bind parameters in error
messages.
-1 allows bind parameters to be printed in full.
If this value is specified without units, it is taken as bytes.
Non-zero values of this setting add overhead, as LightDB will need to store textual representations of parameter values in memory at the start of each statement, whether or not an error eventually occurs. The overhead is greater when bind parameters are sent in binary form than when they are sent as text, since the former case requires data conversion while the latter only requires copying the string.
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.
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_replication_commands (boolean)
Causes each replication command to be logged in the server log.
See Section 49.4 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. If enabled by this setting, a log entry is emitted 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 amount of data. If this value is specified without units, it is taken as 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 in lightdb.conf; lt_initdb
will install a setting there corresponding to its system environment.
See Section 9.4.3 for more information.
This parameter can only be set in the lightdb.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 LightDB source code
(if log_error_verbosity is set to verbose),
application name, and backend type.
Here is a sample table definition for storing CSV-format log output:
CREATE TABLE lightdb_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, backend_type text, PRIMARY KEY (session_id, session_line_num) );
To import a log file into this table, use the COPY FROM
command:
COPY lightdb_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 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.
These settings control how process titles of server processes are modified. Process titles are typically viewed using programs like ps. See Section 26.1 for details.
cluster_name (string)
Sets a name that identifies this database instance (instance) for various purposes. The cluster name appears in the process title for all server processes in this cluster. Moreover, it is the default application name for a standby connection (see synchronous_standby_names.)
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 the
cluster_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.
Only superusers can change this setting.