Configuration

Configure your PostgreSQL cluster & instances according to your needs
Module:
Categories:

You can define different types of instances & clusters.

  • Identity: Parameters used for describing a PostgreSQL cluster
  • Primary: Define a single instance cluster.
  • Replica: Define a basic HA cluster with one primary & one replica.
  • Offline: Define a dedicated instance for OLAP/ETL/Interactive queries
  • Sync Standby: Enable synchronous commit to ensure no data loss.
  • Quorum Commit: Use quorum sync commit for an even higher consistency level.
  • Standby Cluster: Clone an existing cluster and follow it
  • Delayed Cluster: Clone an existing cluster for emergency data recovery
  • Citus Cluster: Define a Citus distributed database cluster
  • Major Version: Create postgres cluster with different major version

Primary

Let’s start with the simplest case, singleton meta:

pg-test:
  hosts:
    10.10.10.11: { pg_seq: 1, pg_role: primary }
  vars:
    pg_cluster: pg-test

Use the following command to create a primary database instance on the 10.10.10.11 node.

bin/pgsql-add pg-test

Replica

To add a physical replica, you can assign a new instance to pg-test with pg_role set to replica

pg-test:
  hosts:
    10.10.10.11: { pg_seq: 1, pg_role: primary }
    10.10.10.12: { pg_seq: 2, pg_role: replica }  # <--- newly added
  vars:
    pg_cluster: pg-test

You can create an entire cluster or append a replica to the existing cluster:

bin/pgsql-add pg-test               # init entire cluster in one-pass
bin/pgsql-add pg-test 10.10.10.12   # add replica to existing cluster

Offline

The offline instance is a dedicated replica to serve slow queries, ETL, OLAP traffic and interactive queries, etc…

To add an offline instance, assign a new instance with pg_role set to offline.

pg-test:
  hosts:
    10.10.10.11: { pg_seq: 1, pg_role: primary }
    10.10.10.12: { pg_seq: 2, pg_role: replica }
    10.10.10.13: { pg_seq: 2, pg_role: offline } # <--- newly added
  vars:
    pg_cluster: pg-test

Offline instance works like common replica instances, but it is used as a backup server in pg-test-replica service. That is to say, offline and primary instance serves only when all replica instances are down.

You can have ad hoc access control offline with pg_default_hba_rules and pg_hba_rules. It will apply to the offline instance and any instances with pg_offline_query flag.

Sync Standby

Pigsty uses asynchronous stream replication by default. Which may have a small replication lag. (10KB / 10ms). A small window of data loss may occur when the primary fails (can be controlled with pg_rpo.), but it is acceptable for most scenarios.

But in some critical scenarios (e.g. financial transactions), data loss is totally unacceptable or read-your-write consistency is required. In this case, you can enable synchronous commit to ensure that.

To enable sync standby mode, you can simply use crit.yml template in pg_conf

pg-test:
  hosts:
    10.10.10.11: { pg_seq: 1, pg_role: primary }
    10.10.10.12: { pg_seq: 2, pg_role: replica }
    10.10.10.13: { pg_seq: 3, pg_role: replica }
  vars:
    pg_cluster: pg-test
    pg_conf: crit.yml   # <--- use crit template

To enable sync standby on existing clusters, config the cluster and enable synchronous_mode:

$ pg edit-config pg-test    # run on admin node with admin user
+++
-synchronous_mode: false    # <--- old value
+synchronous_mode: true     # <--- new value
 synchronous_mode_strict: false

Apply these changes? [y/N]: y

If synchronous_mode: true, the synchronous_standby_names parameter will be managed by patroni. It will choose a sync standby from all available replicas and write its name to the primary’s configuration file.

Quorum Commit

When sync standby is enabled, PostgreSQL will pick one replica as the standby instance, and all other replicas as candidates. Primary will wait until the standby instance flushes to disk before a commit is confirmed, and the standby instance will always have the latest data without any lags.

However, you can achieve an even higher/lower consistency level with the quorum commit (trade-off with availability).

For example, to have all 2 replicas to confirm a commit:

synchronous_mode: true          # make sure synchronous mode is enabled
synchronous_node_count: 2       # at least 2 nodes to confirm a commit

If you have more replicas and wish to have more sync standby, increase synchronous_node_count accordingly. Beware of adjust synchronous_node_count accordingly when you append or remove replicas.

The postgres synchronous_standby_names parameter will be managed by patroni:

synchronous_standby_names = '2 ("pg-test-3","pg-test-2")'
Example: Multiple Sync Standby 
$ pg edit-config pg-test
---
+++
@@ -82,10 +82,12 @@
     work_mem: 4MB
+    synchronous_standby_names: 'ANY 2 (pg-test-2, pg-test-3, pg-test-4)'
 
-synchronous_mode: false
+synchronous_mode: true
+synchronous_node_count: 2
 synchronous_mode_strict: false

Apply these changes? [y/N]: y

And we can see that the two replicas are selected as sync standby now.

+ Cluster: pg-test (7080814403632534854) +---------+----+-----------+-----------------+
| Member    | Host        | Role         | State   | TL | Lag in MB | Tags            |
+-----------+-------------+--------------+---------+----+-----------+-----------------+
| pg-test-1 | 10.10.10.10 | Leader       | running |  1 |           | clonefrom: true |
| pg-test-2 | 10.10.10.11 | Sync Standby | running |  1 |         0 | clonefrom: true |
| pg-test-3 | 10.10.10.12 | Sync Standby | running |  1 |         0 | clonefrom: true |
+-----------+-------------+--------------+---------+----+-----------+-----------------+

The classic quorum commit is to use majority of replicas to confirm a commit.

synchronous_mode: quorum        # use quorum commit
postgresql:
  parameters:                   # change the PostgreSQL parameter `synchronous_standby_names`, use the `ANY n ()` notion
    synchronous_standby_names: 'ANY 1 (*)'  # you can specify a list of standby names, or use `*` to match them all
Example: Enable Quorum Commit 
$ pg edit-config pg-test

+    synchronous_standby_names: 'ANY 1 (*)' # You have to configure this manually
+ synchronous_mode: quorum        # use quorum commit mode, undocumented parameter
- synchronous_node_count: 2       # this parameter is no longer needed in quorum mode

Apply these changes? [y/N]: y

After applying the configuration, we can see that all replicas are no longer sync standby, but just normal replicas.

After that, when we can check pg_stat_replication.sync_state, it becomes quorum instead of sync or async.

Standby Cluster

You can clone an existing cluster and create a standby cluster, which can be used for migration, horizontal split, multi-az deployment, or disaster recovery.

A standby cluster’s definition is just the same as any other normal cluster, except there’s a pg_upstream defined on the primary instance.

For example, you have a pg-test cluster, to create a standby cluster pg-test2, the inventory may look like this:

# pg-test is the original cluster
pg-test:
  hosts:
    10.10.10.11: { pg_seq: 1, pg_role: primary }
  vars: { pg_cluster: pg-test }

# pg-test2 is a standby cluster of pg-test.
pg-test2:
  hosts:
    10.10.10.12: { pg_seq: 1, pg_role: primary , pg_upstream: 10.10.10.11 } # <--- pg_upstream is defined here
    10.10.10.13: { pg_seq: 2, pg_role: replica }
  vars: { pg_cluster: pg-test2 }

And pg-test2-1, the primary of pg-test2 will be a replica of pg-test and serve as a Standby Leader in pg-test2.

Just make sure that the pg_upstream parameter is configured on the primary of the backup cluster to pull backups from the original upstream automatically.

bin/pgsql-add pg-test     # Creating the original cluster
bin/pgsql-add pg-test2    # Creating a Backup Cluster
Example: Change Replication Upstream

You can change the replication upstream of the standby cluster when necessary (e.g. upstream failover).

To do so, just change the standby_cluster.host to the new upstream IP address and apply.

$ pg edit-config pg-test2

 standby_cluster:
   create_replica_methods:
   - basebackup
-  host: 10.10.10.13     # <--- The old upstream
+  host: 10.10.10.12     # <--- The new upstream
   port: 5432

 Apply these changes? [y/N]: y
Example: Promote Standby Cluster

You can promote the standby cluster to a standalone cluster at any time.

To do so, you have to config the cluster and wipe the entire standby_cluster section then apply.

$ pg edit-config pg-test2
-standby_cluster:
-  create_replica_methods:
-  - basebackup
-  host: 10.10.10.11
-  port: 5432

Apply these changes? [y/N]: y
Example: Cascade Replica

If the pg_upstream is specified for replica rather than primary, the replica will be configured as a cascade replica with the given upstream ip instead of the cluster primary

pg-test:
  hosts: # pg-test-1 ---> pg-test-2 ---> pg-test-3
    10.10.10.11: { pg_seq: 1, pg_role: primary }
    10.10.10.12: { pg_seq: 2, pg_role: replica } # <--- bridge instance
    10.10.10.13: { pg_seq: 2, pg_role: replica, pg_upstream: 10.10.10.12 } 
    # ^--- replicate from pg-test-2 (the bridge) instead of pg-test-1 (the primary) 
  vars: { pg_cluster: pg-test }

Delayed Cluster

A delayed cluster is a special type of standby cluster, which is used to recover “drop-by-accident” ASAP.

For example, if you wish to have a cluster pg-testdelay which has the same data as 1-day ago pg-test cluster:

# pg-test is the original cluster
pg-test:
  hosts:
    10.10.10.11: { pg_seq: 1, pg_role: primary }
  vars: { pg_cluster: pg-test }

# pg-testdelay is a delayed cluster of pg-test.
pg-testdelay:
  hosts:
    10.10.10.12: { pg_seq: 1, pg_role: primary , pg_upstream: 10.10.10.11, pg_delay: 1d }
    10.10.10.13: { pg_seq: 2, pg_role: replica }
  vars: { pg_cluster: pg-test2 }

You can also configure a replication delay on the existing standby cluster.

$ pg edit-config pg-testdelay
 standby_cluster:
   create_replica_methods:
   - basebackup
   host: 10.10.10.11
   port: 5432
+  recovery_min_apply_delay: 1h    # <--- add delay here

Apply these changes? [y/N]: y

When some tuples & tables are dropped by accident, you can advance this delayed cluster to a proper time point and select data from it.

It takes more resources, but can be much faster and have less impact than PITR

Citus Cluster

Pigsty has native citus support. Check files/pigsty/citus.yml & prod.yml for example.

To define a citus cluster, you have to specify the following parameters:

Besides, extra hba rules that allow ssl access from local & other data nodes are required. Which may looks like this

all:
  children:
    pg-citus0: # citus data node 0
      hosts: { 10.10.10.10: { pg_seq: 1, pg_role: primary } }
      vars: { pg_cluster: pg-citus0 , pg_group: 0 }
    pg-citus1: # citus data node 1
      hosts: { 10.10.10.11: { pg_seq: 1, pg_role: primary } }
      vars: { pg_cluster: pg-citus1 , pg_group: 1 }
    pg-citus2: # citus data node 2
      hosts: { 10.10.10.12: { pg_seq: 1, pg_role: primary } }
      vars: { pg_cluster: pg-citus2 , pg_group: 2 }
    pg-citus3: # citus data node 3, with an extra replica
      hosts:
        10.10.10.13: { pg_seq: 1, pg_role: primary }
        10.10.10.14: { pg_seq: 2, pg_role: replica }
      vars: { pg_cluster: pg-citus3 , pg_group: 3 }
  vars:                               # global parameters for all citus clusters
    pg_mode: citus                    # pgsql cluster mode: citus
    pg_shard: pg-citus                # citus shard name: pg-citus
    patroni_citus_db: meta            # citus distributed database name
    pg_dbsu_password: DBUser.Postgres # all dbsu password access for citus cluster
    pg_users: [ { name: dbuser_meta ,password: DBUser.Meta ,pgbouncer: true ,roles: [ dbrole_admin ] } ]
    pg_databases: [ { name: meta ,extensions: [ { name: citus }, { name: postgis }, { name: timescaledb } ] } ]
    pg_hba_rules:
      - { user: 'all' ,db: all  ,addr: 127.0.0.1/32 ,auth: ssl ,title: 'all user ssl access from localhost' }
      - { user: 'all' ,db: all  ,addr: intra        ,auth: ssl ,title: 'all user ssl access from intranet'  }

And you can create distributed table & reference table on the coordinator node. Any data node can be used as the coordinator node since citus 11.2.

SELECT create_distributed_table('pgbench_accounts', 'aid'); SELECT truncate_local_data_after_distributing_table($$public.pgbench_accounts$$);
SELECT create_reference_table('pgbench_branches')         ; SELECT truncate_local_data_after_distributing_table($$public.pgbench_branches$$);
SELECT create_reference_table('pgbench_history')          ; SELECT truncate_local_data_after_distributing_table($$public.pgbench_history$$);
SELECT create_reference_table('pgbench_tellers')          ; SELECT truncate_local_data_after_distributing_table($$public.pgbench_tellers$$);

Major Version

Pigsty works on PostgreSQL 10+. While the pre-packaged packages only includes 12 - 16 for now.

version Comment Packages
16 The latest version with important extensions Core, L1 L2
15 The stable major version, with full extension support (default) Core, L1,L2,L3
14 The old stable major version, ith L1 extension support only Core, L1
13 Older major version, with L1 extension support only Core, L1
12 Older major version, with L1 extension support only Core, L1
  • Core: postgresql*, available on PG 12 - 16
  • L1 extensions: wal2json, pg_repack, passwordcheck_cracklib (PG 12 - 16)
  • L2 extensions: postgis, citus, timescaledb, pgvector (PG15, PG16)
  • L3 extensions: Other miscellaneous extensions (PG15 only)

Since some extensions are not available on PG 12,13,14,16, you may have to change pg_extensions and pg_libs to fit your needs.

Here are some example cluster definition with different major versions.

pg-v12:
  hosts: { 10.10.10.12: { pg_seq: 1 ,pg_role: primary } }
  vars:
    pg_cluster: pg-v12
    pg_version: 12
    pg_libs: 'pg_stat_statements, auto_explain'
    pg_extensions: [ 'wal2json_12* pg_repack_12* passwordcheck_cracklib_12*' ]

pg-v13:
  hosts: { 10.10.10.13: { pg_seq: 1 ,pg_role: primary } }
  vars:
    pg_cluster: pg-v13
    pg_version: 13
    pg_libs: 'pg_stat_statements, auto_explain'
    pg_extensions: [ 'wal2json_13* pg_repack_13* passwordcheck_cracklib_13*' ]

pg-v14:
  hosts: { 10.10.10.14: { pg_seq: 1 ,pg_role: primary } }
  vars:
    pg_cluster: pg-v14
    pg_version: 14

pg-v15:
  hosts: { 10.10.10.15: { pg_seq: 1 ,pg_role: primary } }
  vars:
    pg_cluster: pg-v15
    pg_version: 15

pg-v16:
  hosts: { 10.10.10.16: { pg_seq: 1 ,pg_role: primary } }
  vars:
    pg_cluster: pg-v16
    pg_version: 16

Beware that these extensions are just not included in Pigsty’s default repo. You can have these extensions on older pg version with proper configuration.


Last modified 2024-02-29: update content (34b2b75)