The document discusses online upgrades using logical replication in PostgreSQL, specifically through the pglogical extension. It outlines reasons for upgrading, upgrade options, the features and capabilities that can be missed by using older versions, and the steps for installation, configuration, and creating subscriptions. Additionally, it emphasizes testing and provides conclusions on using pglogical as a preferred upgrade method.

1. Online upgrade using
logical replication
Florin Irion
8 December 2020
#postgresbuild2020

2. Whoami?
florin.irion@enterprisedb.com
@irionr

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Agenda
• PostgreSQL releases
• Upgrade options
• What is Pglogical
• Major upgrades

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Why
Upgrade? ● Security
● Features
● Dba/management
● Performance
● SQL standard

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Release
Cadence

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EOL

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About
Minor
Updates

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About
Major
Upgrades
● Logical dump/restore
● Trigger-based replication (not anymore) - e.g.
Londiste
● pg_upgrade
● Native logical streaming replication
○ publisher/subscriber
○ Pglogical extension

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About
Major
Upgrades
● Logical dump/restore
● Trigger-based replication (not anymore) - e.g.
Londiste
● pg_upgrade
● Native logical streaming replication
○ publisher/subscriber
○ Pglogical extension

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Pglogical

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Pglogical
vs
Logical
Replication

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Upgrading
with
pglogical

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What are we
missing by
using
PostgreSQL 9.5?
https://why-upgrade.depesz.com/

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Missing
Features
● Parallel Aggregates
● Parallel sequential scans
● Declarative partitioning
● SCRAM Authentication
● Just In Time (JIT) compilation
● Parallel creation of index
● Stored Procedures
● Reindex concurrently

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Nomenclature
and
conventions
● Node -- Postgresql database instance
● Provider -- sending node
● Subscriber -- receiver node
● Replication Set -- rule
● Subscription -- one subscriber makes to the
provider.
● pg95 pg13 -- my hostnames

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Requirements
● Primary key
● Table schema
● Table definition
● Constraints
● Global objects
● UNLOGGED and TEMPORARY
● DDL
○ replicate_ddl_command()

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Installation
PostgreSQL 9.5: yum install postgresql95-pglogical
PostgreSQL 13: yum install postgresql13-pglogical

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Configuration Postgresql.conf
shared_preload_libraries = 'pglogical'
wal_level = 'logical'
max_worker_processes = 10
max_wal_senders = 10
max_replication_slots = 10

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Pg_hba.conf
Local replication pglogical md5
Local dbname pglogical md5
Host replication pglogical pg13_ip_add/0 md5
Host dbname pglogical pg13_ip_add/0 md5
Authentication

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Create
extension
and nodes
CREATE EXTENSION pglogical;
SELECT pglogical.create_node (
node_name: = 'provider1',
dsn: = 'host = pg95 port = 5432 dbname = db'
);
CREATE EXTENSION pglogical;
SELECT pglogical.create_node (
node_name: = 'subscriber1',
dsn: = 'host = pg13 port = 5432 dbname = db'
);

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Add tables
and
sequences
SELECT pglogical.replication_set_add_all_tables (
set_name := 'default',
schema_names := ARRAY ['public']
);
SELECT pglogical.replication_set_add_all_sequences
(
set_name : = 'default',
schema_names : = ARRAY ['public']
);

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Create
subscription
SELECT pglogical.create_subscription(
subscription_name := 'my_subscription',
provider_dsn := 'host = pg95
port = 5432
dbname = db',
);

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pglogical.create_subscription(
subscription_name name,
provider_dsn text,
replication_sets text[],
synchronize_structure boolean,
synchronize_data boolean,
forward_origins text[],
apply_delay interval
);
Create
subscription

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Check SELECT subscription_name, status
FROM pglogical.show_subscription_status();
subscription_name | status
------------------------+-------------
my_subscription | replicating

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Repeat
CREATE EXTENSION pglogical;
SELECT pglogical.create_node (...'provider'...);
SELECT pglogical.create_node (...'subscriber'...);
SELECT pglogical.create_subscription(...);

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Testing and
application
testing

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Cutover/
Switch

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Post-switch

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Conclusions
• Pglogical is my preferred major upgrade method

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Conclusions
• Start simple and test everything
TEST! TEST! TEST!

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Conclusions
• Pglogical 3
● Replication slot failover support
● REPLICA IDENTITY FULL
● DDL
● Performance
● Kafka and Rabbitmq
● Partitions
● Conflict detection
● Conflict resolution
● No SUPERUSER
● Statistics

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Conclusions
• Kubernetes and Cloud Native friendly

33. Thank you!
Questions?
@irionr
www.enterprisedb.com/contact