This talk cover the most important postgresql.conf variables that users should tune and/or study up on. It is geared toward Postgres 9.0.x servers.

1. The Essential
PostgreSQL.conf
9
Robert Treat, JDCon East 2011
Thursday, March 31, 2011

2. Introduction
• Robert Treat
• OmniTI
• Database Management and Consulting
• Large and/or High Traffic Architectures
• We’re Hiring!
• Postgres
• Web, Advocacy, Conferences, PhpPgAdmin
• Major Contributor
• xzilla.net
• @robtreat2
Thursday, March 31, 2011

3. Introduction
• Robert Treat
• OmniTI
• Database Management and Consulting
• Large and/or High Traffic Architectures
• We’re Hiring!
• Postgres
• Web, Advocacy, Conferences, PhpPgAdmin
• Major Contributor
• xzilla.net
• @robtreat2
Thursday, March 31, 2011

4. The Grand Scheme
• Understanding the postgresql.conf
• Essential postgresql.conf parameters
Thursday, March 31, 2011

5. The Grand Scheme
• Understanding the postgresql.conf
• Essential postgresql.conf parameters
Thursday, March 31, 2011

6. Understanding the postgresql.conf
• Types of Settings
• When Settings Take Effect
• PostgreSQL.conf “Gotchas”
• Viewing Your Current Settings
Thursday, March 31, 2011

7. Types of Settings
Thursday, March 31, 2011

8. Types of Settings
• Boolean: true, false, on, off
Thursday, March 31, 2011

9. Types of Settings
• Boolean: true, false, on, off
• Integer: whole numbers (2112)
Thursday, March 31, 2011

10. Types of Settings
• Boolean: true, false, on, off
• Integer: whole numbers (2112)
• Float: decimal values (21.12)
Thursday, March 31, 2011

11. Types of Settings
• Boolean: true, false, on, off
• Integer: whole numbers (2112)
• Float: decimal values (21.12)
• Memory/Disk Units: 128MB, 2112GB
Thursday, March 31, 2011

12. Types of Settings
• Boolean: true, false, on, off
• Integer: whole numbers (2112)
• Float: decimal values (21.12)
• Memory/Disk Units: 128MB, 2112GB
• Avoid using integers to size memory parameters
Thursday, March 31, 2011

13. Types of Settings
• Boolean: true, false, on, off
• Integer: whole numbers (2112)
• Float: decimal values (21.12)
• Memory/Disk Units: 128MB, 2112GB
• Avoid using integers to size memory parameters
• Time: d,m,s (30s)
Thursday, March 31, 2011

14. Types of Settings
• Boolean: true, false, on, off
• Integer: whole numbers (2112)
• Float: decimal values (21.12)
• Memory/Disk Units: 128MB, 2112GB
• Avoid using integers to size memory parameters
• Time: d,m,s (30s)
• Strings: single quotes (‘pg_log’)
Thursday, March 31, 2011

15. Types of Settings
• Boolean: true, false, on, off
• Integer: whole numbers (2112)
• Float: decimal values (21.12)
• Memory/Disk Units: 128MB, 2112GB
• Avoid using integers to size memory parameters
• Time: d,m,s (30s)
• Strings: single quotes (‘pg_log’)
• Enum: single quotes (‘WARNING’ or ‘ERROR’)
Thursday, March 31, 2011

16. Types of Settings
• Boolean: true, false, on, off
• Integer: whole numbers (2112)
• Float: decimal values (21.12)
• Memory/Disk Units: 128MB, 2112GB
• Avoid using integers to size memory parameters
• Time: d,m,s (30s)
• Strings: single quotes (‘pg_log’)
• Enum: single quotes (‘WARNING’ or ‘ERROR’)
• Limited set of acceptable strings
Thursday, March 31, 2011

17. Types of Settings
• Boolean: true, false, on, off
• Integer: whole numbers (2112)
• Float: decimal values (21.12)
• Memory/Disk Units: 128MB, 2112GB
• Avoid using integers to size memory parameters
• Time: d,m,s (30s)
• Strings: single quotes (‘pg_log’)
• Enum: single quotes (‘WARNING’ or ‘ERROR’)
• Limited set of acceptable strings
• Lists: comma seperated (‘“$user”,public,tsearch2’)
Thursday, March 31, 2011

18. When Settings Take Effect
• Internal: set at compile time
• Postmaster: requires database restart
• Backend: must be set before session start
• Sighup: change by reloading conf file
• pg_reload_conf(), pg_ctl reload, kill -HUP
• Superuser: set at runtime by superuser
• User: set at runtime, affects only a single session
See pg_settings.context to determine setting type
Thursday, March 31, 2011

19. When Settings Take Effect
• Internal: set at compile time
• Postmaster: requires database restart
• Backend: must be set before session start
• Sighup: change by reloading conf file
• pg_reload_conf(), pg_ctl reload, kill -HUP
• Superuser: set at runtime by superuser
• User: set at runtime, affects only a single session
See pg_settings.context to determine setting type
Thursday, March 31, 2011

20. postgresql.conf Gotchas!
• Where is my postgresql.conf ?
• $PGDATA/postgresql.conf
• watch out for symbolic links
• some distros put it in other places (/etc)
• SHOW data_directory;
• SHOW config_file;
Thursday, March 31, 2011

21. postgresql.conf Gotchas!
• Lines with #
• This line is a comment, and has no effect
• On a fresh install, uses defaults
• Commenting a line is the same as deleting a line,
it will restore the “default” for that instance
Thursday, March 31, 2011

22. Viewing Your Current Settings
• Look in postgresql.conf
• Works if you follow best practices
• Not definitive!
Thursday, March 31, 2011

23. Viewing Your Current Settings
• Look in postgresql.conf
• Works if you follow best practices
• Not definitive!
• SHOW ALL, SHOW <setting>,
current_setting(setting)
• Shows the current value
• Watch out for session specific changes
Thursday, March 31, 2011

24. Viewing Your Current Settings
• Look in postgresql.conf
• Works if you follow best practices
• Not definitive!
• SHOW ALL, SHOW <setting>,
current_setting(setting)
• Shows the current value
• Watch out for session specific changes
• SELECT * FROM pg_settings
• Shows the current value
• “source” column
Thursday, March 31, 2011

25. Viewing Your Current Settings
pagila=# select current_setting(name), * from pg_settings
where name = 'shared_buffers';
-[ RECORD 1 ]------+----------------------------------------------
current_setting | 1600kB
name | shared_buffers
setting | 200
unit | 8kB
category | Resource Usage / Memory
short_desc | Sets the number of shared memory buffers used by the server.
extra_desc |
context | postmaster
vartype | integer
source | configuration file
min_val | 16
max_val | 1073741823
enumvals |
boot_val | 1024
reset_val | 200
sourcefile | /opt/local/var/db/postgresql91/data/postgresql.conf
sourceline | 109
Thursday, March 31, 2011

26. The Essential Parameters
• Logging
• Getting Connected
• Sizing Memory
• Checkpoint Management
• Vacuum Managment
• WAL management
Thursday, March 31, 2011

27. Logging
• log_destination, log_directory, log_filename
• find out where you are logging
• might be good to log to a different disk than your data
Thursday, March 31, 2011

28. Logging
• log_destination, log_directory, log_filename
• find out where you are logging
• might be good to log to a different disk than your data
• log_line_prefix
• generic recommendation: ‘%t: %r: %u@%d: [%p]: ‘
• timestamp, connecting host, username, database, pid
Thursday, March 31, 2011

29. Get Connected
• listen_addresses
• requires restart!
• default is localhost only
• use * to enable tcp/ip
Thursday, March 31, 2011

30. Get Connected
• listen_addresses
• requires restart!
• default is localhost only
• use * to enable tcp/ip
• max_connections
• requires restart!
• 100 default (apache children default is higher)
• affects other settings (work_mem)
• for 1000+ connections, use connection pooler
Thursday, March 31, 2011

31. Sizing Memory
• shared_buffers
• requires restart!
• most important setting for good performance
• allocation of memory for Postgres caching
• ~20% of Total Available RAM (up to 2GB)
• 32GB RAM, 1920 MB is probably ok
• 256GB RAM, 50 GB is probably not optimal
• Windows users probably want less
• may require adjusting kernel params (shmmax)
• http://www.postgresql.org/docs/current/interactive/kernel-resources.html
Thursday, March 31, 2011

32. Sizing Memory
• effective_cache_size
• most important setting for good performance
• based on memory available for filesystem cache
• SET = TRAM - (DRAM - PGRAM)
• TRAM = Total RAM
• DRAM = RAM needed by OS and other apps
• PGRAM = RAM needed for Postgres (shared_buffers, etc...)
• Guide for available memory, not an allocation
Thursday, March 31, 2011

33. Sizing Memory
• work_mem
• used by queries for sorting
• higher values for more complex queries
• limit is per sort
• 5 sorts in 1 query = 5*work_mem
• maintenance_work_mem
• used by vacuum, indexing, and similar operations
• semi-allocation of memory when needed
• don’t be scared to make this big (1GB)
Thursday, March 31, 2011

34. Checkpoint Management
• checkpoint_segments
• controls the amount of data required per checkpoint
• default 3, recommended minimum of 10
• set higher for heavy write activity
• 30 - 300 is not uncommon
• increases space needed in pg_xlog
• increases recovery time after crash
• checkpoint_completion_target
• with checkpoint_segments >= 10, set this to .9
• http://www.westnet.com/~gsmith/content/postgresql/chkp-bgw-83.htm
Thursday, March 31, 2011

35. Vacuum Management
• autovacuum
• max_fsm_pages
• max_fsm_relations
• default_statistics_target
• autovacuum_freeze_max_age
• set to 1,000,000,000 to reduce vacuums for non-activity
• requires restart
Thursday, March 31, 2011

36. WAL Management / Replication
• WAL for Performance
• wal_buffers
• requires restart!
• needed for write heavy loads
• 16MB, “set it and forget it!”
• synchronous_commit
• can increase tps by a large margin
• allows data loss without corruption
• BAD: fsync = off
• GOOD: synchronous_commit = off
• can be set per database, user, or transaction
Thursday, March 31, 2011

37. WAL Management / Replication
• WAL for Replication
• wal_level
• requires restart!
• “hot_standby” needed for... hot standbys
• max_wal_senders
• requires restart!
• controls the number of connections for streaming
replication
Thursday, March 31, 2011

38. The End
Thanks!
Additional Resources
http://www.postgresql.org/docs/current/interactive/runtime-config.html
http://wiki.postgresql.org/wiki/Tuning_Your_PostgreSQL_Server
Slides
http://www.xzilla.net/writings.html
Thursday, March 31, 2011

39. No Really, The End
Thursday, March 31, 2011