Contents

• pg_sqlog
  • Description
  • Prerequisites
  • Tables
  • Functions
  • Installation
  • Examples
  • Querying slave node logs

pg_sqlog

An extension providing access to PostgreSQL logs through SQL interface.

Description

pg_sqlog allows to query a foreign table, pointing to a log, recorded in a CSV format. It has special functions to extract the query duration of each query, as well as to group similar queries together.

Prerequisites

Set log_min_duration_statement to a non-negative value in order to record the slow queries.

log_min_duration_statement = 1000 # logs every query taking more than 1 second

This extension depends on file_fdw as well as on the following configuration directives.

log_destination = 'syslog,csvlog' # 'csvlog' should be present log_filename = 'postgresql.%F' # any combination of %F, %Y, %m, %d, %a logging_collector = 'on' log_rotation_age = '1d' # at max 1 log file per day log_rotation_size = 0 log_truncate_on_rotation = 'on'

To use the special autovacuum and autoanalyze reports you need to set log_autovacuum_min_duration to a non-negative value.

log_autovacuum_min_duration = 0

Tables

• sqlog.log - a template table, pointing to a log file, generated through a given day. It could be either queried through the special sqlog.log() set of function, or directly in a combination with the sqlog.set_date() function. By default the date is set to the last call to sqlog.log() or sqlog.set_date().

Functions

• sqlog.log([timestamp]) - a set returning function, giving the contents of the PostgreSQL log file for a given day. If interval is omitted, then the current day's log is returned. Calls sqlog.set_date() implicitly.
• sqlog.set_date([timestamp]) - a function to control the sqlog.log filename option. Once set to a given date, it stays that way until another call to it. Note that calling this function will influence the contents of the sqlog.log table for all the other concurrent sessions as well (if any).
• sqlog.duration(text) - extracts the query duration from the message field in milliseconds.
• sqlog.preparable_query(text) - replaces all the possible arguments of a query found in the message field with question marks, thus providing a preparable query, effectively grouping similar queries together.
• sqlog.temporary_file_size(text) - extracts the file size of each temporary file that has been created and logged, according to the log_temp_files configuration option. Pass sqlog.message as argument.
• sqlog.autovacuum([timestamp]) - a set returning function, giving human readable report of the autovacuum runs for a given day. Calls sqlog.set_date() implicitly.
• sqlog.autoanalyze([timestamp]) - a set returning function, giving human readable report of the autoanalyze runs for a given day. Calls sqlog.set_date() implicitly.

Installation

After making the project, copy the conf/pg_sqlog.conf file to the conf.d/ PostgreSQL directory (or make the appropriate changes to your postgresql.conf file directly) and restart the service.

Examples

Get a summary of the errors reported for the day.

postgres=# SELECT error_severity, COUNT(*) FROM sqlog.log() GROUP BY 1; error_severity | count ----------------+------- FATAL | 6 WARNING | 27 LOG | 949 ERROR | 10 (4 rows)

Get the top 3 slowest queries of the day.

``` SELECT AVG(sqlog.duration(message)), COUNT(*), sqlog.preparable_query(message) FROM sqlog.log() WHERE message ~ '^duration' GROUP BY 3 ORDER BY 2 DESC LIMIT 3;

                   preparable_query                       |          avg          | count

--------------------------------------------------------------+-----------------------+------- SELECT pg_sleep(?) | 9002.774 | 2 SELECT id, name FROM invoice WHERE status > ? | 4367.3729834738293848 | 12 UPDATE app SET credit=?+overdraft WHERE id=? and overdraft>? | 1158.1232790697674419 | 43 (3 rows) ```

Get a random autovacuum report for the day.

postgres=# select * from sqlog.autovacuum() limit 1; -[ RECORD 1 ]-------------+--------------------------- log_time | 2018-11-06 06:03:00.178+00 database | db schema_name | public table_name | account idx_scans | 1 pages_removed | 1 pages_remain | 16 pages_skipped_pins | 0 pages_skipped_frozen | 0 tuples_removed | 455 tuples_remain | 27 tuples_dead_not_removable | 0 oldest_xmin | 224250521 buffer_hits | 187 buffer_misses | 0 buffer_dirtied | 7 read_mbs | 0.000 write_mbs | 0.033 cpu_user | 0.04 cpu_system | 0.02 elapsed | 1.64

Querying slave node logs

Analyzing queries on a slave node is also possible. In order to change the date make a call to sqlog.set_date([date]) on the master node prior to querying sqlog.log on the slave.