Administration

How to maintain an existing PostgreSQL cluster with Pigsty?

Here are some SOP for common pgsql admin tasks

Case 1: Create Cluster
Case 2: Create User
Case 3: Create Database
Case 4: Reload Service
Case 5: Reload HBARule
Case 6: Config Cluster
Case 7: Append Replica
Case 8: Remove Replica
Case 9: Remove Cluster
Case 10: Switchover
Case 11: Backup Cluster
Case 12: Restore Cluster
Case 13: Adding Packages
Case 14: Install Extension
Case 15: Minor Upgrade
Case 16: Major Upgrade

Cheatsheet

PGSQL playbooks and shortcuts:

bin/pgsql-add   <cls>                   # create pgsql cluster <cls>
bin/pgsql-user  <cls> <username>        # create pg user <username> on <cls>
bin/pgsql-db    <cls> <dbname>          # create pg database <dbname> on <cls>
bin/pgsql-svc   <cls> [...ip]           # reload pg service of cluster <cls>
bin/pgsql-hba   <cls> [...ip]           # reload postgres/pgbouncer HBA rules of cluster <cls>
bin/pgsql-add   <cls> [...ip]           # append replicas for cluster <cls>
bin/pgsql-rm    <cls> [...ip]           # remove replicas from cluster <cls>
bin/pgsql-rm    <cls>                   # remove pgsql cluster <cls>

Patroni admin command and shortcuts:

pg list        <cls>                    # print cluster info
pg edit-config <cls>                    # edit cluster config
pg reload      <cls> [ins]              # reload cluster config
pg restart     <cls> [ins]              # restart pgsql cluster
pg reinit      <cls> [ins]              # reinit cluster members
pg pause       <cls>                    # entering maintenance mode (no auto failover)
pg resume      <cls>                    # exiting maintenance mode
pg switchover  <cls>                    # switchover on cluster <cls>
pg failover    <cls>                    # failover on cluster <cls>

pgBackRest backup & restore command and shortcuts:

pb info                                 # print pgbackrest repo info
pg-backup                               # make a backup, incr, or full backup if necessary
pg-backup full                          # make a full backup
pg-backup diff                          # make a differential backup
pg-backup incr                          # make a incremental backup
pg-pitr -i                              # restore to the time of latest backup complete (not often used)
pg-pitr --time="2022-12-30 14:44:44+08" # restore to specific time point (in case of drop db, drop table)
pg-pitr --name="my-restore-point"       # restore TO a named restore point create by pg_create_restore_point
pg-pitr --lsn="0/7C82CB8" -X            # restore right BEFORE a LSN
pg-pitr --xid="1234567" -X -P           # restore right BEFORE a specific transaction id, then promote
pg-pitr --backup=latest                 # restore to latest backup set
pg-pitr --backup=20221108-105325        # restore to a specific backup set, which can be checked with pgbackrest info

Systemd components quick reference

systemctl stop patroni                  # start stop restart reload
systemctl stop pgbouncer                # start stop restart reload
systemctl stop pg_exporter              # start stop restart reload
systemctl stop pgbouncer_exporter       # start stop restart reload
systemctl stop node_exporter            # start stop restart
systemctl stop haproxy                  # start stop restart reload
systemctl stop vip-manager              # start stop restart reload
systemctl stop postgres                 # only when patroni_mode == 'remove'

Create Cluster

To create a new Postgres cluster, define it in the inventory first, then init with:

bin/node-add <cls>                # init nodes for cluster <cls>           # ./node.yml  -l <cls>
bin/pgsql-add <cls>               # init pgsql instances of cluster <cls>  # ./pgsql.yml -l <cls>

Beware, perform bin/node-add first, then bin/pgsql-add, PGSQL works on managed nodes only.

Create User

To create a new business user on the existing Postgres cluster, add user definition to all.children.<cls>.pg_users, then create the user as follows:

bin/pgsql-user <cls> <username>   # ./pgsql-user.yml -l <cls> -e username=<username>

Create Database

To create a new database user on the existing Postgres cluster, add database definition to all.children.<cls>.pg_databases, then create the database as follows:

bin/pgsql-db <cls> <dbname>       # ./pgsql-db.yml -l <cls> -e dbname=<dbname>

Note: If the database has specified an owner, the user should already exist, or you’ll have to Create User first.

Reload Service

Services are exposed access point served by HAProxy.

This task is used when cluster membership has changed, e.g., append/remove replicas, switchover/failover / exposing new service or updating existing service’s config (e.g., LB Weight)

To create new services or reload existing services on entire proxy cluster or specific instances:

bin/pgsql-svc <cls>               # pgsql.yml -l <cls> -t pg_service -e pg_reload=true
bin/pgsql-svc <cls> [ip...]       # pgsql.yml -l ip... -t pg_service -e pg_reload=true

Reload HBARule

This task is used when your Postgres/Pgbouncer HBA rules have changed, you may have to reload hba to apply changes.

If you have any role-specific HBA rules, you may have to reload hba after a switchover/failover, too.

To reload postgres & pgbouncer HBA rules on entire cluster or specific instances:

bin/pgsql-hba <cls>               # pgsql.yml -l <cls> -t pg_hba,pg_reload,pgbouncer_hba,pgbouncer_reload -e pg_reload=true
bin/pgsql-hba <cls> [ip...]       # pgsql.yml -l ip... -t pg_hba,pg_reload,pgbouncer_hba,pgbouncer_reload -e pg_reload=true

Config Cluster

To change the config of a existing Postgres cluster, you have to initiate control command on admin node with admin user:

pg edit-config <cls>              # interactive config a cluster with patronictl

Change patroni parameters & postgresql.parameters, save & apply changes with the wizard.

Append Replica

To add a new replica to the existing Postgres cluster, you have to add its definition to the inventory: all.children.<cls>.hosts, then:

bin/node-add <ip>                 # init node <ip> for the new replica
bin/pgsql-add <cls> <ip>          # init pgsql instances on <ip> for cluster <cls>

It will add node <ip> to pigsty and init it as a replica of the cluster <cls>.

Cluster services will be reloaded to adopt the new member

Remove Replica

To remove a replica from the existing PostgreSQL cluster:

bin/pgsql-rm <cls> <ip...>        # ./pgsql-rm.yml -l <ip>

It will remove instance <ip> from cluster <cls>. Cluster services will be reloaded to kick the removed instance from load balancer.

Remove Cluster

To remove the entire Postgres cluster, just run:

bin/pgsql-rm <cls>                # ./pgsql-rm.yml -l <cls>

Switchover

You can perform a PostgreSQL cluster switchover with patroni cmd.

pg switchover <cls>   # interactive mode, you can skip that with following options
pg switchover --leader pg-test-1 --candidate=pg-test-2 --scheduled=now --force pg-test

Backup Cluster

To create a backup with pgBackRest, run as local dbsu:

pg-backup                         # make a postgres base backup
pg-backup full                    # make a full backup
pg-backup diff                    # make a differential backup
pg-backup incr                    # make a incremental backup
pb info                           # check backup information

Check Backup & PITR for details.

Restore Cluster

To restore a cluster to a previous time point (PITR), run as local dbsu:

pg-pitr -i                              # restore to the time of latest backup complete (not often used)
pg-pitr --time="2022-12-30 14:44:44+08" # restore to specific time point (in case of drop db, drop table)
pg-pitr --name="my-restore-point"       # restore TO a named restore point create by pg_create_restore_point
pg-pitr --lsn="0/7C82CB8" -X            # restore right BEFORE a LSN
pg-pitr --xid="1234567" -X -P           # restore right BEFORE a specific transaction id, then promote
pg-pitr --backup=latest                 # restore to latest backup set
pg-pitr --backup=20221108-105325        # restore to a specific backup set, which can be checked with pgbackrest info

And follow the instructions wizard, Check Backup & PITR for details.

Adding Packages

To add newer version of RPM packages, you have to add them to repo_packages and repo_url_packages

Then rebuild repo on infra nodes with ./infra.yml -t repo_build subtask, Then you can install these packages with ansible module package:

ansible pg-test -b -m package -a "name=pg_cron_15,topn_15,pg_stat_monitor_15*"  # install some packages

Install Extension

If you want to install extension on pg clusters, Add them to pg_extensions and make sure them installed with:

./pgsql.yml -t pg_extension     # install extensions

Some extension needs to be loaded in shared_preload_libraries, You can add them to pg_libs, or Config an existing cluster.

Finally, CREATE EXTENSION <extname>; on the cluster primary instance to install it.

Check PGSQL Extensions: Install for details.

Minor Upgrade

To perform a minor server version upgrade/downgrade, you have to add packages to yum/apt repo first.

Then perform a rolling upgrade/downgrade from all replicas, then switchover the cluster to upgrade the leader.

ansible <cls> -b -a "yum upgrade/downgrade -y <pkg>"    # upgrade/downgrade packages
pg restart --force <cls>                                # restart cluster

Major Upgrade

The simplest way to achieve a major version upgrade is to create a new cluster with the new version, then migration with logical replication & green/blue deployment.

You can also perform an in-place major upgrade, which is not recommended especially when certain extensions are installed. But it is possible.

Assume you want to upgrade PostgreSQL 14 to 15, you have to add packages to yum/apt repo, and guarantee the extensions has exact same version too.

./pgsql.yml -t pg_pkg -e pg_version=15                         # install packages for pg 15
sudo su - postgres; mkdir -p /data/postgres/pg-meta-15/data/   # prepare directories for 15
pg_upgrade -b /usr/pgsql-14/bin/ -B /usr/pgsql-15/bin/ -d /data/postgres/pg-meta-14/data/ -D /data/postgres/pg-meta-15/data/ -v -c # preflight
pg_upgrade -b /usr/pgsql-14/bin/ -B /usr/pgsql-15/bin/ -d /data/postgres/pg-meta-14/data/ -D /data/postgres/pg-meta-15/data/ --link -j8 -v -c
rm -rf /usr/pgsql; ln -s /usr/pgsql-15 /usr/pgsql;             # fix binary links
mv /data/postgres/pg-meta-14 /data/postgres/pg-meta-15         # rename data directory
rm -rf /pg; ln -s /data/postgres/pg-meta-15 /pg                # fix data dir links

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