Log Management - PostgreSQL

 standard error --> stderr

log_destination='stderr'

This can be on or off, and when on, collects stderr output into a configured log directory.

logging_collector=on

log_directory='capegemini_log'

log_filename='capegemini-%Y-%m-%d_%H%M%S.log'

log_rotation_age='1d'

log_rotation_size='10MB'

log_destination = 'stderr'   # Valid values are combinations of
                             # stderr, csvlog, syslog, and eventlog,
                             # depending on platform.  csvlog
                             # requires logging_collector to be on.


# This is used when logging to stderr:
logging_collector = on       # Enable capturing of stderr and csvlog
                             # into log files. Required to be on for
                             # csvlogs.
                             # (change requires restart)


# These are only used if logging_collector is on:
log_directory = 'pg_log'     # directory where log files are written,
                             # can be absolute or relative to PGDATA


log_filename = 'postgresql-%Y-%m-%d_%H%M%S.log' # log file name pattern,
                                        # can include strftime() escapes

log_file_mode = 0600            # creation mode for log files,
                                # begin with 0 to use octal notation

log_truncate_on_rotation = off  # If on, an existing log file with the
                    # same name as the new log file will be
                    # truncated rather than appended to.
                    # But such truncation only occurs on
                    # time-driven rotation, not on restarts
                    # or size-driven rotation.  Default is
                    # off, meaning append to existing files
                    # in all cases.

log_rotation_age = 1d  # Automatic rotation of logfiles will
                    # happen after that time.  0 disables.

log_rotation_size = 10MB  # Automatic rotation of logfiles will
                    # happen after that much log output.
                    # 0 disables.

Notes: 

Will there be a performance impact by enabling PostgreSQL logging?

R&D did some testing with the following settings:

in the postgresql.conf file:
log_destination = 'csvlog'
logging_collector = on
log_connections = on
log_disconnections = on
log_hostname = on
log_statement = 'all'
log_line_prefix = '%a%%%u%%%s'

 
R&D's statement from their testing:

Average response time:
Slightly higher with logging enabled but the biggest difference was only 4ms. Average time without logging 163ms, with logging 166ms.

Processor time:
PostgreSQL used very little CPU time. Average time without logging was 0.29%, with logging 0.33%.

Memory usage:
Here, slightly less memory was used with logging enabled. Average without logging 1.16GB, with logging 1.13GB.

Log files on disk:
With logging enabled, a number of files were created on the local disk. About 10MB of data were created every minute.

The conclusion from the tests: that it is safe to enable the logs in PostgreSQL. The only thing that needs attention is to make sure the log files do not fill up the storage.