PostgreSQL Replication has multiple approaches. This webinar presentation will help you understand the differences between multiple replication approaches, the requirements of each strategy, and what can be achieved with each of them, so you will make a more informed decision on what's best to adopt for your system. This webinar presentation covers: - How physical replication works in PostgreSQL - How logical replication works in PostgreSQL - Differences between synchronous and asynchronous replication - Advantages, disadvantages, and challenges in multi-master replication - Which replication strategy is more suitable to different use cases

1. A Review of PostgreSQL
Replication Approaches
Boriss Mejías
Solution Architect
Air Guitar Player
@tchorix
25 February 2021

2. Why this Talk?

3. Open Source Music
By Kiko Loureiro
https://gt.kikoloureiro.com/open-source/

5. Heavy Metal has its roots in Blues & Rock
Replication has its roots in Backup & Recovery
Variations from the roots

6. PostgreSQL resilient to crash

7. Physical backup and recovery

8. Read replica

9. Is it master or replica?
On master
boa=# select pg_is_in_recovery();
pg_is_in_recovery
-------------------
f
On replica
boa=# select pg_is_in_recovery();
pg_is_in_recovery
-------------------
t

10. Can you hear me !?
boa=# select * from pg_stat_replication;
-[ RECORD 1 ]----+------------------------------
pid | 14284
application_name | mumbai
client_addr | 172.17.0.3
state | streaming
sent_lsn | 0/3049320
write_lsn | 0/3049320
flush_lsn | 0/3049320
replay_lsn | 0/3049320
write_lag | 00:00:00.000628
flush_lag | 00:00:00.001741
replay_lag | 00:00:00.00224
sync_priority | 0
sync_state | async

11. Physical streaming replication

15. Asynchronous replication

16. Multiple replicas

17. Horizontal read scalability

18. Robustness with two locations

19. Cascading replication

20. Such a fine line between cascading...
bangalore is primary
at beijing node
primary_conninfo='user=repmgr host=bangalore port=5432 application_name=beijing'
at sydney node
primary_conninfo='user=repmgr host=beijing port=5432 application_name=sydney'

21. Add a witness

22. Automated failover

23. Automated failover – network or node failure

24. Automated failover – network isolation

25. Protect against human error

26. Delayed physical streaming replication

27. Reduce data loss → synchronous replication

28. Lag really matters now
boa=# select * from pg_stat_replication;
-[ RECORD 1 ]----+------------------------------
pid | 14284
application_name | mumbai
client_addr | 172.17.0.3
state | streaming
sent_lsn | 0/3049320
write_lsn | 0/3049320
flush_lsn | 0/3049320
replay_lsn | 0/3049320
write_lag | 00:00:00.000628
flush_lag | 00:00:00.001741
replay_lag | 00:00:00.00224
sync_priority | 1
sync_state | sync

29. Who is replicating?
boa=# select * from pg_stat_replication;
-[ RECORD 1 ]----+------------------------------
pid | 14284
application_name | mumbai synchronous_standby_names
client_addr | 172.17.0.3
state | streaming
sent_lsn | 0/3049320
write_lsn | 0/3049320
flush_lsn | 0/3049320
replay_lsn | 0/3049320
write_lag | 00:00:00.000628
flush_lag | 00:00:00.001741
replay_lag | 00:00:00.00224
sync_priority | 1
sync_state | sync

30. When is synchronously replicated?
boa=# select * from pg_stat_replication;
-[ RECORD 1 ]----+------------------------------
pid | 14284
application_name | mumbai synchronous_standby_names
client_addr | 172.17.0.3
state | streaming
sent_lsn | 0/3049320
write_lsn | 0/3049320 remote_write
flush_lsn | 0/3049320 on
replay_lsn | 0/3049320 remote_apply
write_lag | 00:00:00.000628
flush_lag | 00:00:00.001741
replay_lag | 00:00:00.00224
sync_priority | 1
sync_state | sync

31. Reduce data loss → synchronous replication

32. Reduce data loss → synchronous replication

33. Synchronous standby names

34. Synchronous standby names
synchronous_standby_names = ...
'FIRST 1 (beijing, mumbai, jakarta)'
'FIRST 2 (mumbai, jakarta, beijing)'
'ANY 2 (mumbai, jakarta, beijing)'

35. Different places to be synchronous
synchronous_commit = ...
remote_write
on
remote_apply
local

36. Synchronous when it’s important
synchronous_standby_names = 'ANY 1 (mumbai, jakarta, beijing)'
synchronous_commit = local

37. Synchronous when it’s important
synchronous_standby_names = 'ANY 1 (mumbai, jakarta, beijing)'
synchronous_commit = local
boa=# SET synchronous_commit = remote_apply;
SET
boa=# INSERT INTO orders (id, customer, item, quantity)
VALUES (2267709, 999, 'beer', 18);
INSERT 0 1
boa=# RESET synchronous_commit ;
RESET

38. Synchronous Replication - Fragile

39. Synchronous Replication - OK

40. Synchronous Replication – 2 DC

41. Synchronous Replication – 2 DC

42. Synchronous Replication - Robust

43. Dynamic asynchronous / synchronous

44. Intermezzo

46. Physical streaming replication

47. Logical streaming replication

48. Logical streaming replication

49. Upgrade major version

50. Upgrade major version and split

51. Upgrade full cluster

52. Upgrade full cluster

53. Upgrade full cluster

54. Progressive Metal

59. Conclusion

61. Open Source Community
It brings us a higher sense of community and
enhances our creativity and possibilities.
So why not take this concept to our art, our
music?
- Kiko Loureiro

62. A Review of PostgreSQL
Replication Approaches
Thank you
boriss.mejias@enterprisedb.com
@tchorix