This talk is prepared as a bunch of slides, where each slide describes a really bad way people can screw up their PostgreSQL database and provides a weight - how frequently I saw that kind of problem. Right before the talk I will reshuffle the deck to draw twenty random slides and explain you why such practices are bad and how to avoid running into them.

1. PostgreSQL
worst practices
Ilya Kosmodemiansky
ik@dataegret.com

2. Best practices are just boring
• Never follow them, try worst practices
• Only worst practices can really help you screw things up in a
most effective way
• PostgreSQL consultants are nice people - keep them happy!
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

3. How it works?
• I have a list, a little bit more than 100 worst practices
• I do not make this stuff up, all of them are real-life examples
• I reshuffle my list every time before presenting and pick a few
examples
• Well, there are some things, which I like more or less, so it is
not a very honest shuffle
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

4. 0. Do not use indexes (a test one!)
• Basically, there is no difference between full table scan and
index scan
• You can check that. Just insert 10 rows into a test table on
your test server and compare.
• Nobody deals with more than 10 row tables in production!
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

5. 1. Use as many count(*) as you can
• Figure 301083021830123921 is very informative for the end
user
• If it changes in a second to 30108302894839434020, it is still
informative
• select count(*) from sometable is a quite light-weighted query
• Tuple estimation from pg_catalog can never be precise
enough to you
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

6. 2. Use ORM
• All databases share the same syntax
• You must write database-independent code
• Are there any benefits, which are based on database specific
features?
• It always good to learn a new complicated technology
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

7. 3. Move joins to your application
• Just select * a couple of tables into the application written in
your favorite programming language
• Than join them at the application level
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

8. 3. Move joins to your application
• Just select * a couple of tables into the application written in
your favorite programming language
• Than join them at the application level
• Now you only need to implement nested loop join, hash join
and merge join as well as query optimizer and page cache
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

9. 4. Be in trend, be schema-less
• You do not need to design the schema
• You only need one table, two columns: id bigserial and extra
jsonb
• JSONB datatype is pretty effective in PostgreSQL, you can
query it just like a well-structured table
• Even if you put a 100M of JSON in it
• Even if you have 1000+ tps
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

10. 5. Be agile, use EAV
• You only need 3 tables: entity, attribute, value
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

11. 5. Be agile, use EAV
• You only need 3 tables: entity, attribute, value
• At some point add the 4th: attribute_type
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

12. 5. Be agile, use EAV
• You only need 3 tables: entity, attribute, value
• At some point add the 4th: attribute_type
• When it starts slowing down, just call those four tables The
Core and add 1000+ tables with denormalized data
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

13. 5. Be agile, use EAV
• You only need 3 tables: entity, attribute, value
• At some point add the 4th: attribute_type
• When it starts slowing down, just call those four tables The
Core and add 1000+ tables with denormalized data
• If it is not enough, you can always add value_version
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

14. 6. Try to create as many indexes as you can
• Indexes consume no disk space
• Indexes consume no shared_bufers
• There is no overhead on DML if one and every column in a
table covered with bunch of indexes
• Optimizer will definitely choose your index once you created it
• Keep calm and create more indexes
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

15. 7. Always keep all your time series data
• Time series data like tables with logs or session history should
never be deleted, aggregated or archived, you always need to
keep it all
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

16. 7. Always keep all your time series data
• Time series data like tables with logs or session history should
never be deleted, aggregated or archived, you always need to
keep it all
• You will always know where to check, if you run out of disk
space
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

17. 7. Always keep all your time series data
• Time series data like tables with logs or session history should
never be deleted, aggregated or archived, you always need to
keep it all
• You will always know where to check, if you run out of disk
space
• You can always call that Big Data
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

18. 7. Always keep all your time series data
• Time series data like tables with logs or session history should
never be deleted, aggregated or archived, you always need to
keep it all
• You will always know where to check, if you run out of disk
space
• You can always call that Big Data
• Solve the problem using partitioning... one partition for an
hour or for a minute
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

19. 8. Turn autovacuum off
• It is quite auxiliary process, you can easily stop it
• There is no problem at all to have 100Gb data in a database
which is 1Tb in size
• 2-3Tb RAM servers are cheap, IO is a fastest thing in modern
computing
• Besides, everyone likes BigData
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

20. 9. Reinvent Slony
• If you need some data replication to another database, try to
implement it from scratch
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

21. 9. Reinvent Slony
• If you need some data replication to another database, try to
implement it from scratch
• That allows you to run into all sorts of problems PostgreSQL
had since introducing Slony
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

22. 10. Keep master and slave on different hardware
• That will maximize the possibility of unsuccessful failover
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

23. 10. Keep master and slave on different hardware
• That will maximize the possibility of unsuccessful failover
• To make things even worse, you can change only slave-related
parameters at slave, leaving defaults for shared_buffers etc.
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

24. 11. Put a synchronous replica to remote DC
• Indeed! That will maximize availability!
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

25. 11. Put a synchronous replica to remote DC
• Indeed! That will maximize availability!
• Especially, if you put the replica to another continent
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

26. 12. Never use Foreign Keys
• Consistency control at application level always works as
expected
• You will never get data inconsistency without constraints
• Even if you already have a bullet proof framework to maintain
consistency, could it be good enough reason to use it?
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

27. 13. Always use text type for all columns
• It is always fun to reimplement date or ip validation in your
code
• You will never mistakenly convert ”12-31-2015 03:01AM” to
”15:01 12 of undef 2015” using text fields
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

28. 14. Always use improved ”PostgreSQL”
• Postgres is not a perfect database and you are smart
• All that annoying MVCC staff, 32 bit xid and autovacuum
nightmares look the way they do because hackers are oldschool
and lazy
• Hack it in a hard way, do not bother submitting your patch to
the community, just put it into production
• It is easy to maintain such production and keep it compatible
with ”not perfect” PostgreSQL upcoming versions
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

29. 15. Postgres likes long transactions
• Always call external services from stored procedures (like
sending emails)
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

30. 15. Postgres likes long transactions
• Always call external services from stored procedures (like
sending emails)
• Oh, it is arguable... It can be, if 100% of developers were
familiar with word timeout
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

31. 15. Postgres likes long transactions
• Always call external services from stored procedures (like
sending emails)
• Oh, it is arguable... It can be, if 100% of developers were
familiar with word timeout
• Anyway, you can just start transaction and go away for a
weekend
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

32. 16. Never read your code, write it!
genre_id IN
( SELECT id FROM genres WHERE genres.id IN
(SELECT * FROM unnest(array[155]))
)
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

33. 17. Have problems with you PostgreSQL installation?
• Move those problems to the container!
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

34. 17. Have problems with you PostgreSQL installation?
• Move those problems to the container!
• It is always good to have something very stable inside
something very unstable!
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

35. 17. Have problems with you PostgreSQL installation?
• Move those problems to the container!
• It is always good to have something very stable inside
something very unstable!
• Now your problems are both inside and outside!
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

36. 17. Not only Slony should be reinvented!
• Need to convert timestamp? Stored procedure in C will help!
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

37. 17. Not only Slony should be reinvented!
• Need to convert timestamp? Stored procedure in C will help!
• Need a message queue? Write it!
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

38. 17. Not only Slony should be reinvented!
• Need to convert timestamp? Stored procedure in C will help!
• Need a message queue? Write it!
• Won’t use ORM? Write your own in plpgsql
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

39. 18. And never, never use exceptions
• Documentation says they are slow
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

40. 18. And never, never use exceptions
• Documentation says they are slow
• Raise notice on errors - everyone reads logs constantly!
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

41. 18. And never, never use exceptions
• Documentation says they are slow
• Raise notice on errors - everyone reads logs constantly!
• Who cares about errors?
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

42. 19. Application runs out of connections?
• Set max_connections to 1000
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

43. 19. Application runs out of connections?
• Set max_connections to 1000
• Common, servers with 1000 CPUs are cheap now
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

44. 19. Application runs out of connections?
• Set max_connections to 1000
• Common, servers with 1000 CPUs are cheap now
• Who said PostgreSQL workers have some overhead?
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

45. 19. Application runs out of connections?
• Set max_connections to 1000
• Common, servers with 1000 CPUs are cheap now
• Who said PostgreSQL workers have some overhead?
• And never ever use pgbouncer!
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

46. 20. Use pgpool-II instead
• Pooling connections with pgpool is easy...
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

47. 20. Use pgpool-II instead
• Pooling connections with pgpool is easy...
• Just like writing a code in that Emacs OS...
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

48. 20. Use pgpool-II instead
• Pooling connections with pgpool is easy...
• Just like writing a code in that Emacs OS...
• Simple config, useful features
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

49. 20. Use pgpool-II instead
• Pooling connections with pgpool is easy...
• Just like writing a code in that Emacs OS...
• Simple config, useful features
• Consulters are happy!
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

50. 21. Always start tuning PostgreSQL...
• From optimizer options in postgresql.conf
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

51. 21. Always start tuning PostgreSQL...
• From optimizer options in postgresql.conf
• Forget about those shared_buffers and checkpoints!
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

52. 21. Always start tuning PostgreSQL...
• From optimizer options in postgresql.conf
• Forget about those shared_buffers and checkpoints!
• geqo options are a good candidate to be a silver bullet!
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

53. 22. Have heard about a cool new feature?
• Use it in production immediately!
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

54. 22. Have heard about a cool new feature?
• Use it in production immediately!
• Attend MVCC Unmasked by Bruce Momjian (Today, 15:50,
Liberty I)
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

55. 22. Have heard about a cool new feature?
• Use it in production immediately!
• Attend MVCC Unmasked by Bruce Momjian (Today, 15:50,
Liberty I)
• Learn about xmin and xmax
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

56. 22. Have heard about a cool new feature?
• Use it in production immediately!
• Attend MVCC Unmasked by Bruce Momjian (Today, 15:50,
Liberty I)
• Learn about xmin and xmax
• Use it in your applications logic!
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

57. Do not forget
That was WORST practices talk
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com

58. Send me your favourite!
ik@dataegret.com
dataegret.com
Why this talk
• Linux is a most common OS for databases
• DBAs often run into IO problems
• Most of the information on topic is written by kerneldevelopers
(for kernel developers) or is checklist-style
• Checklists are useful, but up to certain workload
dataegret.com