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Chapter 9. Database servers

9.1. Introduction to database servers

A database server is a service that provides features of a database management system (DBMS). DBMS provides utilities for database administration and interacts with end users, applications, and databases.

Red Hat Enterprise Linux 8 provides the following database management systems:

  • MariaDB 10.3
  • MariaDB 10.5 - available since RHEL 8.4
  • MySQL 8.0
  • PostgreSQL 10
  • PostgreSQL 9.6
  • PostgreSQL 12 - available since RHEL 8.1.1
  • PostgreSQL 13 - available since RHEL 8.4

9.2. Using MariaDB

9.2.1. Getting started with MariaDB

The MariaDB server is an open source fast and robust database server that is based on the MySQL technology.

MariaDB is a relational database that converts data into structured information and provides an SQL interface for accessing data. It includes multiple storage engines and plug-ins, as well as geographic information system (GIS) and JavaScript Object Notation (JSON) features.

This part describes:

9.2.2. Installing MariaDB

In RHEL 8, the MariaDB server is available in the following versions, each provided by a separate stream:

  • MariaDB 10.3
  • MariaDB 10.5 - available since RHEL 8.4

To install MariaDB, use the following procedure.

Procedure

  1. Install MariaDB server packages by selecting a stream (version) from the mariadb module and specifying the server profile. For example: 

    # yum module install mariadb:10.3/server

  2. Start the mariadb service: 

    # systemctl start mariadb.service

  3. Enable the mariadb service to start at boot: 

    # systemctl enable mariadb.service

  4. Recommended: To improve security when installing MariaDB, run the following command: 

    # mysql_secure_installation

    The command launches a fully interactive script, which prompts for each step in the process. The script enables you to improve security in the following ways:

    • Setting a password for root accounts
    • Removing anonymous users
    • Disallowing remote root logins (outside the local host)
Note

The MariaDB and MySQL database servers cannot be installed in parallel in RHEL 8 due to conflicting RPM packages. Parallel installation of components is possible in Red Hat Software Collections for RHEL 7. In RHEL 8, different versions of database servers can be used in containers.

9.2.3. Configuring MariaDB

To configure the MariaDB server for networking, use the following procedure.

Procedure

  1. Edit the [mysqld] section of the /etc/my.cnf.d/mariadb-server.cnf file. You can set the following configuration directives:

    • bind-address - is the address on which the server listens. Possible options are:

      • a host name
      • an IPv4 address
      • an IPv6 address

    • skip-networking - controls whether the server listens for TCP/IP connections. Possible values are:

      • 0 - to listen for all clients
      • 1 - to listen for local clients only
    • port - the port on which MariaDB listens for TCP/IP connections.

  2. Restart the mariadb service: 

    # systemctl restart mariadb.service

9.2.4. Backing up MariaDB data

There are two main ways to back up data from a MariaDB database:

  • Logical backup
  • Physical backup

Logical backup consists of the SQL statements necessary to restore the data. This type of backup exports information and records in plain text files.

The main advantage of logical backup over physical backup is portability and flexibility. The data can be restored on other hardware configurations, MariaDB versions or Database Management System (DBMS), which is not possible with physical backups.

Note that logical backup can be performed if the mariadb.service is running. Logical backup does not include log and configuration files.

Physical backup consists of copies of files and directories that store the content.

Physical backup has the following advantages compared to logical backup:

  • Output is more compact.
  • Backup is smaller in size.
  • Backup and restore are faster.
  • Backup includes log and configuration files.

Note that physical backup must be performed when the mariadb.service is not running or all tables in the database are locked to prevent changes during the backup.

You can use one of the following MariaDB backup approaches to back up data from a MariaDB database:

  • Logical backup with mysqldump
  • Physical online backup using the Mariabackup utility
  • File system backup
  • Replication as a backup solution

9.2.4.1. Performing logical backup with mysqldump

The mysqldump client is a backup utility, which can be used to dump a database or a collection of databases for the purpose of a backup or transfer to another database server. The output of mysqldump typically consists of SQL statements to re-create the server table structure, populate it with data, or both. mysqldump can also generate files in other formats, including XML and delimited text formats, such as CSV.

To perform the mysqldump backup, you can use one of the following options:

  • Back up one or more selected databases
  • Back up a subset of tables from one database
  • Back up all databases

Procedure

  • To dump an entire database, run: 

    # mysqldump [options] db_name > backup-file.sql

  • To dump a subset of tables from one database, add a list of the chosen tables at the end of the mysqldump command: 

    # mysqldump [options] db_name [tbl_name …​] > backup-file.sql

  • To load the dump file back into a server, use either of these commands: 

    # mysql db_name < backup-file.sql
    # mysql -e "source /path-to-backup/backup-file.sql" db_name

  • To populate databases by copying data from one MariaDB server to another, run: 

    # mysqldump --opt db_name | mysql --host=remote_host -C db_name

  • To dump multiple databases at once, run: 

    # mysqldump [options] --databases db_name1 [db_name2 …​] > my_databases.sql

  • To dump all databases, run: 

    # mysqldump [options] --all-databases > all_databases.sql

  • To see a list of the options that mysqldump supports, run: 

    $ mysqldump --help

Additional resources

9.2.4.2. Performing physical online backup using the Mariabackup utility

Mariabackup is a utility based on the Percona XtraBackup technology, which enables performing physical online backups of InnoDB, Aria, and MyISAM tables. This utility is provided by the mariadb-backup package from the AppStream repository.

Mariabackup supports full backup capability for MariaDB server, which includes encrypted and compressed data.

Prerequisites

  • The mariadb-backup package is installed on the system: 

    # yum install mariadb-backup
  • You must provide Mariabackup with credentials for the user under which the backup will be run. You can provide the credentials either on the command line or by a configuration file.
  • Users of Mariabackup must have the RELOAD, LOCK TABLES, and REPLICATION CLIENT privileges.

To create a backup of a database using Mariabackup, use the following procedure.

Procedure

  • To create a backup while providing credentials on the command line, run: 

    $ mariabackup --backup --target-dir <backup_directory> --user <backup_user> --password <backup_passwd>

    The target-dir option defines the directory where the backup files are stored. If you want to perform a full backup, the target directory must be empty or not exist.

    The user and password options allow you to configure the user name and the password.

  • To create a backup with credentials set in a configuration file:

    1. Create a configuration file in the /etc/my.cnf.d/ directory, for example, /etc/my.cnf.d/mariabackup.cnf.

    2. Add the following lines into the [xtrabackup] or [mysqld] section of the new file: 

      [xtrabackup]
user=myuser
password=mypassword

    3. Perform the backup: 

      $ mariabackup --backup --target-dir <backup_directory>
Important

Mariabackup does not read options in the [mariadb] section of configuration files. If a non-default data directory is specified on a MariaDB server, you must specify this directory in the [xtrabackup] or [mysqld] sections of configuration files so that Mariabackup is able to find the data directory.

To specify a non-default data directory, include the following line in the [xtrabackup] or [mysqld] sections of MariaDB configuration files: 

datadir=/var/mycustomdatadir

Additional resources

9.2.4.3. Restoring data using the Mariabackup utility

When the backup is complete, you can restore the data from the backup by using the mariabackup command with one of the following options:

  • --copy-back allows you to keep the original backup files.
  • --move-back moves the backup files to the data directory and removes the original backup files.

To restore data using the Mariabackup utility, use the following procedure.

Prerequisites

  • Make sure that the mariadb service is not running: 

    # systemctl stop mariadb.service
  • Make sure that the data directory is empty.
  • Users of Mariabackup must have the RELOAD, LOCK TABLES, and REPLICATION CLIENT privileges.

Procedure

  1. Run the mariabackup command:

    • To restore data and keep the original backup files, use the --copy-back option: 

      $ mariabackup --copy-back --target-dir=/var/mariadb/backup/

    • To restore data and remove the original backup files, use the --move-back option: 

      $ mariabackup --move-back --target-dir=/var/mariadb/backup/

  2. Fix the file permissions.

    When restoring a database, Mariabackup preserves the file and directory privileges of the backup. However, Mariabackup writes the files to disk as the user and group restoring the database. After restoring a backup, you may need to adjust the owner of the data directory to match the user and group for the MariaDB server, typically mysql for both.

    For example, to recursively change ownership of the files to the mysql user and group: 

    # chown -R mysql:mysql /var/lib/mysql/

  3. Start the mariadb service: 

    # systemctl start mariadb.service

Additional resources

9.2.4.4. Performing file system backup

To create a file system backup of MariaDB data files, switch to the root user and copy the content of the MariaDB data directory to your backup location.

To back up also your current configuration or the log files, use the optional steps of the following procedure.

Procedure

  1. Stop the mariadb service: 

    # systemctl stop mariadb.service

  2. Copy the data files to the required location: 

    # cp -r /var/lib/mysql /backup-location

  3. Optionally, copy the configuration files to the required location: 

    # cp -r /etc/my.cnf /etc/my.cnf.d /backup-location/configuration

  4. Optionally, copy the log files to the required location: 

    # cp /var/log/mariadb/* /backup-location/logs

  5. Start the mariadb service: 

    # systemctl start mariadb.service

9.2.4.5. Replication as a backup solution

Replication is an alternative backup solution for source servers. If a source server replicates to a replica server, backups can be run on the replica without any impact on the source. The source can still run while you shut down the replica and back the data up from the replica.

Warning

Replication itself is not a sufficient backup solution. Replication protects source servers against hardware failures, but it does not ensure protection against data loss. It is recommended that you use any other backup solution on the replica together with this method.

Additional resources

9.2.5. Migrating to MariaDB 10.3

RHEL 7 contains MariaDB 5.5 as the default implementation of a server from the MySQL databases family. Later versions of the MariaDB database server are available as Software Collections for RHEL 7. RHEL 8 provides MariaDB 10.3, MariaDB 10.5, and MySQL 8.0.

This part describes migration to MariaDB 10.3 from a RHEL 7 or Red Hat Software Collections version of MariaDB. If you want to migrate from MariaDB 10.3 to MariaDB 10.5 within RHEL 8, see Upgrading from MariaDB 10.3 to MariaDB 10.5 instead.

9.2.5.1. Notable differences between the RHEL 7 and RHEL 8 versions of MariaDB

The most important changes between MariaDB 5.5 and MariaDB 10.3 are as follows:

  • MariaDB Galera Cluster, a synchronous multi-source cluster, is a standard part of MariaDB since 10.1.
  • The ARCHIVE storage engine is no longer enabled by default, and the plug-in needs to be specifically enabled.
  • The BLACKHOLE storage engine is no longer enabled by default, and the plug-in needs to be specifically enabled.

  • InnoDB is used as the default storage engine instead of XtraDB, which was used in MariaDB 10.1 and earlier versions.

    For more details, see Why does MariaDB 10.2 use InnoDB instead of XtraDB?.

  • The new mariadb-connector-c packages provide a common client library for MySQL and MariaDB. This library is usable with any version of the MySQL and MariaDB database servers. As a result, the user is able to connect one build of an application to any of the MySQL and MariaDB servers distributed with Red Hat Enterprise Linux 8.

To migrate from MariaDB 5.5 to MariaDB 10.3, you need to perform multiple configuration changes as described in Section 9.2.5.2, “Configuration changes”.

9.2.5.2. Configuration changes

The recommended migration path from MariaDB 5.5 to MariaDB 10.3 is to upgrade to MariaDB 10.0 first, and then upgrade by one version successively.

The main advantage of upgrading one minor version at a time is better adaptation of the database, including both data and configuration, to the changes. The upgrade ends on the same major version as is available in RHEL 8 (MariaDB 10.3), which significantly reduces configuration changes or other issues.

For more information about configuration changes when migrating from MariaDB 5.5 to MariaDB 10.0, see Migrating to MariaDB 10.0 in Red Hat Software Collections documentation.

The migration to following successive versions of MariaDB and the required configuration changes is described in these documents:

Note

Migration directly from MariaDB 5.5 to MariaDB 10.3 is also possible, but you must perform all configuration changes that are required by differences described in the migration documents above.

9.2.5.3. In-place upgrade using the mysql_upgrade utility

To migrate the database files to RHEL 8, users of MariaDB on RHEL 7 must perform the in-place upgrade using the mysql_upgrade utility. The mysql_upgrade utility is provided by the mariadb-server-utils subpackage, which is installed as a dependency of the mariadb-server package.

To perform an in-place upgrade, you must copy binary data files to the /var/lib/mysql/ data directory on the RHEL 8 system and use the mysql_upgrade utility.

You can use this method for migrating data from:

  • The Red Hat Enterprise Linux 7 version of MariaDB 5.5

  • The Red Hat Software Collections versions of:

    • MariaDB 5.5 (no longer supported)
    • MariaDB 10.0 (no longer supported)
    • MariaDB 10.1 (no longer supported)
    • MariaDB 10.2 (no longer supported)

    • MariaDB 10.3

      Note that it is recommended to upgrade to MariaDB 10.3 by one version successively. See the respective Migration chapters in the Release Notes for Red Hat Software Collections.

Note

If you are upgrading from the RHEL 7 version of MariaDB, the source data is stored in the /var/lib/mysql/ directory. In case of Red Hat Software Collections versions of MariaDB, the source data directory is /var/opt/rh/<collection_name>/lib/mysql/ (with the exception of the mariadb55, which uses the /opt/rh/mariadb55/root/var/lib/mysql/ data directory).

To perform an upgrade using the mysql_upgrade utility, use the following procedure.

Prerequisites

  • Before performing the upgrade, back up all your data stored in the MariaDB databases.

Procedure

  1. Ensure that the mariadb-server package is installed on the RHEL 8 system: 

    # yum install mariadb-server

  2. Ensure that the mariadb service is not running on either of the source and target systems at the time of copying data: 

    # systemctl stop mariadb.service
  3. Copy the data from the source location to the /var/lib/mysql/ directory on the RHEL 8 target system.

  4. Set the appropriate permissions and SELinux context for copied files on the target system: 

    # restorecon -vr /var/lib/mysql

  5. Start the MariaDB server on the target system: 

    # systemctl start mariadb.service

  6. Run the mysql_upgrade command to check and repair internal tables: 

    # mysql_upgrade
  7. When the upgrade is complete, make sure that all configuration files within the /etc/my.cnf.d/ directory include only options valid for MariaDB 10.3.
Important

There are certain risks and known problems related to an in-place upgrade. For example, some queries might not work or they will be run in different order than before the upgrade. For more information on these risks and problems, and for general information about an in-place upgrade, see MariaDB 10.3 Release Notes.

9.2.6. Upgrading from MariaDB 10.3 to MariaDB 10.5

This part describes migration from MariaDB 10.3 to MariaDB 10.5 within RHEL 8.

9.2.6.1. Notable differences between MariaDB 10.3 and MariaDB 10.5

Significant changes between MariaDB 10.3 and MariaDB 10.5 include:

  • MariaDB now uses the unix_socket authentication plug-in by default. The plug-in enables users to use operating system credentials when connecting to MariaDB through the local Unix socket file.
  • MariaDB adds mariadb-* named binaries and mysql* symbolic links pointing to the mariadb-* binaires. For example, the mysqladmin, mysqlaccess, and mysqlshow symlinks point to the mariadb-admin, mariadb-access, and mariadb-show binaries, respectively.
  • The SUPER privilege has been split into several privileges to better align with each user role. As a result, certain statements have changed required privileges.
  • In parallel replication, the slave_parallel_mode now defaults to optimistic.
  • In the InnoDB storage engine, defaults of the following variables have been changed: innodb_adaptive_hash_index to OFF and innodb_checksum_algorithm to full_crc32.

  • MariaDB now uses the libedit implementation of the underlying software managing the MariaDB command history (the .mysql_history file) instead of the previously used readline library. This change impacts users working directly with the .mysql_history file. Note that .mysql_history is a file managed by the MariaDB or MySQL applications, and users should not work with the file directly. The human-readable appearance is coincidental.

    Note

    To increase security, you can consider not maintaining a history file. To disable the command history recording:

    1. Remove the .mysql_history file if it exists.

    2. Use either of the following approaches:

      • Set the MYSQL_HISTFILE variable to /dev/null and include this setting in any of your shell’s startup files.

      • Change the .mysql_history file to a symbolic link to /dev/null: 

        $ ln -s /dev/null $HOME/.mysql_history

MariaDB Galera Cluster has been upgraded to version 4 with the following notable changes:

  • Galera adds a new streaming replication feature, which supports replicating transactions of unlimited size. During an execution of streaming replication, a cluster replicates a transaction in small fragments.
  • Galera now fully supports Global Transaction ID (GTID).
  • The default value for the wsrep_on option in the /etc/my.cnf.d/galera.cnf file has changed from 1 to 0 to prevent end users from starting wsrep replication without configuring required additional options.

Changes to the PAM plug-in in MariaDB 10.5 include:

  • MariaDB 10.5 adds a new version of the Pluggable Authentication Modules (PAM) plug-in. The PAM plug-in version 2.0 performs PAM authentication using a separate setuid root helper binary, which enables MariaDB to utilize additional PAM modules.
  • The helper binary can be executed only by users in the mysql group. By default, the group contains only the mysql user. Red Hat recommends that administrators do not add more users to the mysql group to prevent password-guessing attacks without throttling or logging through this helper utility.
  • In MariaDB 10.5, the Pluggable Authentication Modules (PAM) plug-in and its related files have been moved to a new package, mariadb-pam. As a result, no new setuid root binary is introduced on systems that do not use PAM authentication for MariaDB.
  • The mariadb-pam package contains both PAM plug-in versions: version 2.0 is the default, and version 1.0 is available as the auth_pam_v1 shared object library.
  • The mariadb-pam package is not installed by default with the MariaDB server. To make the PAM authentication plug-in available in MariaDB 10.5, install the mariadb-pam package manually.

9.2.6.2. Upgrading from a RHEL 8 version of MariaDB 10.3 to MariaDB 10.5

This procedure describes upgrading from the mariadb:10.3 module stream to the mariadb:10.5 module stream using the yum and mariadb-upgrade utilities.

The mariadb-upgrade utility is provided by the mariadb-server-utils subpackage, which is installed as a dependency of the mariadb-server package.

Prerequisites

  • Before performing the upgrade, back up all your data stored in the MariaDB databases.

Procedure

  1. Stop the MariaDB server: 

    # systemctl stop mariadb.service

  2. Execute the following command to determine if your system is prepared for switching to a later stream: 

    # yum distro-sync

    This command must finish with the message Nothing to do. Complete! For more information, see Switching to a later stream.

  3. Reset the mariadb module on your system: 

    # yum module reset mariadb

  4. Enable the new mariadb:10.5 module stream: 

    # yum module enable mariadb:10.5

  5. Synchronize installed packages to perform the change between streams: 

    # yum distro-sync

    This will update all installed MariaDB packages.

  6. Adjust configuration so that option files located in /etc/my.cnf.d/ include only options valid for MariaDB 10.5. For details, see upstream documentation for MariaDB 10.4 and MariaDB 10.5.

  7. Start the MariaDB server.

    • When upgrading a database running standalone: 

      # systemctl start mariadb.service

    • When upgrading a Galera cluster node: 

      # galera_new_cluster

      The mariadb service will be started automatically.

  8. Execute the mariadb-upgrade utility to check and repair internal tables.

    • When upgrading a database running standalone: 

      # mariadb-upgrade

    • When upgrading a Galera cluster node: 

      # mariadb-upgrade --skip-write-binlog
Important

There are certain risks and known problems related to an in-place upgrade. For example, some queries might not work or they will be run in different order than before the upgrade. For more information on these risks and problems, and for general information about an in-place upgrade, see MariaDB 10.5 Release Notes.

9.2.7. Replicating MariaDB with Galera

This section describes how to replicate a MariaDB database using the Galera solution.

9.2.7.1. Introduction to MariaDB Galera Cluster

Galera replication is based on the creation of a synchronous multi-source MariaDB Galera Cluster consisting of multiple MariaDB servers. Unlike the traditional primary/replica setup where replicas are usually read-only, nodes in the MariaDB Galera Cluster can be all writable.

The interface between Galera replication and a MariaDB database is defined by the write set replication API (wsrep API).

The main features of MariaDB Galera Cluster are:

  • Synchronous replication
  • Active-active multi-source topology
  • Read and write to any cluster node
  • Automatic membership control, failed nodes drop from the cluster
  • Automatic node joining
  • Parallel replication on row level
  • Direct client connections: users can log on to the cluster nodes, and work with the nodes directly while the replication runs

Synchronous replication means that a server replicates a transaction at commit time by broadcasting the write set associated with the transaction to every node in the cluster. The client (user application) connects directly to the Database Management System (DBMS), and experiences behavior that is similar to native MariaDB.

Synchronous replication guarantees that a change that happened on one node in the cluster happens on other nodes in the cluster at the same time.

Therefore, synchronous replication has the following advantages over asynchronous replication:

  • No delay in propagation of the changes between particular cluster nodes
  • All cluster nodes are always consistent
  • The latest changes are not lost if one of the cluster nodes crashes
  • Transactions on all cluster nodes are executed in parallel
  • Causality across the whole cluster

Additional resources

For more detailed information, see the upstream documentation:

9.2.7.2. Components to build MariaDB Galera Cluster

To build MariaDB Galera Cluster, you must install the following packages on your system:

  • mariadb-server-galera - contains support files and scripts for MariaDB Galera Cluster.
  • mariadb-server - is patched by MariaDB upstream to include the write set replication API (wsrep API). This API provides the interface between Galera replication and MariaDB.

  • galera - is patched by MariaDB upstream to add full support for MariaDB. The galera package contains the following:

    • Galera Replication Library - provides the whole replication functionality.
    • The Galera Arbitrator utility - can be used as a cluster member that participates in voting in split-brain scenarios. However, Galera Arbitrator cannot participate in the actual replication.

Additional resources

For more detailed information, see upstream documentation:

9.2.7.3. Deploying MariaDB Galera Cluster

Prerequisites

  • Install MariaDB Galera Cluster packages by selecting a stream (version) from the mariadb module and specifying the galera profile. For example: 

    # yum module install mariadb:10.3/galera

    As a result, the following packages are installed:

  • The MariaDB server replication configuration must be updated before the system is added to a cluster for the first time.

    The default configuration is distributed in the /etc/my.cnf.d/galera.cnf file.

    Before deploying MariaDB Galera Cluster, set the wsrep_cluster_address option in the /etc/my.cnf.d/galera.cnf file on all nodes to start with the following string: 

    gcomm://

    • For the initial node, it is possible to set wsrep_cluster_address as an empty list: 

      wsrep_cluster_address="gcomm://"

    • For all other nodes, set wsrep_cluster_address to include an address to any node which is already a part of the running cluster. For example: 

      wsrep_cluster_address="gcomm://10.0.0.10"

      For more information on how to set Galera Cluster address, see Galera Cluster Address.

Procedure

  1. Bootstrap a first node of a new cluster by running the following wrapper on that node: 

    # galera_new_cluster

    This wrapper ensures that the MariaDB server daemon (mysqld) runs with the --wsrep-new-cluster option. This option provides the information that there is no existing cluster to connect to. Therefore, the node creates a new UUID to identify the new cluster.

    Note

    The mariadb service supports a systemd method for interacting with multiple MariaDB server processes. Therefore, in cases with multiple running MariaDB servers, you can bootstrap a specific instance by specifying the instance name as a suffix: 

    # galera_new_cluster mariadb@node1

  2. Connect other nodes to the cluster by running the following command on each of the nodes: 

    # systemctl start mariadb

    As a result, the node connects to the cluster, and synchronizes itself with the state of the cluster.

Additional resources

9.2.7.4. Adding a new node to MariaDB Galera Cluster

To add a new node to MariaDB Galera Cluster, use the following procedure.

Note that you can also use this procedure to reconnect an already existing node.

Procedure

  • On the particular node, provide an address to one or more existing cluster members in the wsrep_cluster_address option within the [mariadb] section of the /etc/my.cnf.d/galera.cnf configuration file : 

    [mariadb]
wsrep_cluster_address="gcomm://192.168.0.1"

    When a new node connects to one of the existing cluster nodes, it is able to see all nodes in the cluster.

    However, preferably list all nodes of the cluster in wsrep_cluster_address.

    As a result, any node can join a cluster by connecting to any other cluster node, even if one or more cluster nodes are down. When all members agree on the membership, the cluster’s state is changed. If the new node’s state is different from the state of the cluster, the new node requests either an Incremental State Transfer (IST) or a State Snapshot Transfer (SST) to ensure consistency with the other nodes.

Additional resources

9.2.7.5. Restarting MariaDB Galera Cluster

If you shut down all nodes at the same time, you terminate the cluster, and the running cluster no longer exists. However, the cluster’s data still exist.

To restart the cluster, bootstrap a first node as described in Section 9.2.7.3, “Deploying MariaDB Galera Cluster”.

Warning

If the cluster is not bootstrapped, and mysqld on the first node is started with only the systemctl start mariadb command, the node tries to connect to at least one of the nodes listed in the wsrep_cluster_address option in the /etc/my.cnf.d/galera.cnf file. If no nodes are currently running, the restart fails.

Additional resources

9.3. Using PostgreSQL

9.3.1. Getting started with PostgreSQL

The PostgreSQL server is an open source robust and highly-extensible database server based on the SQL language. It provides an object-relational database system, which allows you to manage extensive datasets and a high number of concurrent users. For these reasons, the PostgreSQL servers can be used in clusters to manage high amounts of data.

The PostgreSQL server includes features for ensuring data integrity, building fault-tolerant environments, and building applications. It allows users to extend a database with users' own data types, custom functions, or code from different programming languages without the need to recompile the database.

This part describes:

9.3.2. Installing PostgreSQL

In RHEL 8, the PostgreSQL server is available in several versions, each provided by a separate stream:

  • PostgreSQL 10 - the default stream
  • PostgreSQL 9.6
  • PostgreSQL 12 - available since RHEL 8.1.1
  • PostgreSQL 13 - available since RHEL 8.4
Note

By design, it is impossible to install more than one version (stream) of the same module in parallel. Thus you must choose only one of the available streams from the postgresql module. Parallel installation of components is possible in Red Hat Software Collections for RHEL 7. In RHEL 8, different versions of database servers can be used in containers.

To install PostgreSQL, use the following procedure.

Procedure

  1. Install the PostgreSQL server packages by selecting a stream (version) from the postgresql module and specifying the server profile. For example: 

    # yum module install postgresql:13/server

    The postgres superuser is created automatically.

  2. Initialize the database cluster: 

    # postgresql-setup --initdb

    Red Hat recommends storing the data in the default /var/lib/pgsql/data directory.

  3. Start the postgresql service: 

    # systemctl start postgresql.service

  4. Enable the postgresql service to start at boot: 

    # systemctl enable postgresql.service

For information about using module streams, see Installing, managing, and removing user-space components.

Important

If you want to upgrade from an earlier postgresql stream within RHEL 8, follow both procedures described in Switching to a later stream and in Section 9.3.6, “Migrating to a RHEL 8 version of PostgreSQL”.

9.3.3. PostgreSQL users

PostgreSQL users are of the following types:

  • The postgres UNIX system user - should be used only to run the PostgreSQL server and client applications, such as pg_dump. Do not use the postgres system user for any interactive work on PostgreSQL administration, such as database creation and user management.
  • A database superuser - the default postgres PostgreSQL superuser is not related to the postgres system user. You can limit access of the postgres superuser in the pg_hba.conf file, otherwise no other permission limitations exist. You can also create other database superusers.

  • A role with specific database access permissions:

    • A database user - has a permission to log in by default
    • A group of users - enables managing permissions for the group as a whole

Roles can own database objects (for example, tables and functions) and can assign object privileges to other roles using SQL commands.

Standard database management privileges include SELECT, INSERT, UPDATE, DELETE, TRUNCATE, REFERENCES, TRIGGER, CREATE, CONNECT, TEMPORARY, EXECUTE, and USAGE.

Role attributes are special privileges, such as LOGIN, SUPERUSER, CREATEDB, and CREATEROLE.

Important

Red Hat recommends performing most tasks as a role that is not a superuser. A common practice is to create a role that has the CREATEDB and CREATEROLE privileges and use this role for all routine management of databases and roles.

Additional resources

9.3.4. Configuring PostgreSQL

In a PostgreSQL database, all data and configuration files are stored in a single directory called a database cluster. Red Hat recommends storing all data in the default /var/lib/pgsql/data/ directory.

PostgreSQL configuration consists of the following files:

  • postgresql.conf - is used for setting the database cluster parameters.
  • postgresql.auto.conf - holds basic PostgreSQL settings similarly to postgresql.conf. However, this file is under the server control. It is edited by the ALTER SYSTEM queries, and cannot be edited manually.
  • pg_ident.conf - is used for mapping user identities from external authentication mechanisms into the PostgreSQL user identities.
  • pg_hba.conf - is used for configuring client authentication for PostgreSQL databases.

To change the PostgreSQL configuration, use the following procedure.

Procedure

  1. Edit the respective configuration file, for example, /var/lib/pgsql/data/postgresql.conf.

  2. Restart the postgresql service so that the changes become effective: 

    # systemctl restart postgresql.service

Example 9.1. Configuring PostgreSQL database cluster parameters

This example shows basic settings of the database cluster parameters in the /var/lib/pgsql/data/postgresql.conf file. 

# This is a comment
log_connections = yes
log_destination = 'syslog'
search_path = '"$user", public'
shared_buffers = 128MB

Example 9.2. Setting client authentication in PostgreSQL

This example demonstrates how to set client authentication in the /var/lib/pgsql/data/pg_hba.conf file. 

# TYPE    DATABASE       USER        ADDRESS              METHOD
local     all            all                              trust
host      postgres       all         192.168.93.0/24      ident
host      all            all         .example.com         scram-sha-256

9.3.5. Backing up PostgreSQL data

To back up PostgreSQL data, use one of the following approaches:

9.3.5.1. Backing up PostgreSQL data with an SQL dump

The SQL dump method is based on generating a dump file with SQL commands. When a dump is uploaded back to the database server, it recreates the database in the same state as it was at the time of the dump.

The SQL dump is ensured by the following PostgreSQL client applications:

  • pg_dump dumps a single database without cluster-wide information about roles or tablespaces
  • pg_dumpall dumps each database in a given cluster and preserves cluster-wide data, such as role and tablespace definitions.

By default, the pg_dump and pg_dumpall commands write their results into the standard output. To store the dump in a file, redirect the output to an SQL file. The resulting SQL file can be either in a text format or in other formats that allow for parallelism and for more detailed control of object restoration.

You can perform the SQL dump from any remote host that has access to the database.

9.3.5.1.1. Advantages and disadvantages of an SQL dump

An SQL dump has the following advantages compared to other PostgreSQL backup methods:

  • An SQL dump is the only PostgreSQL backup method that is not server version-specific. The output of the pg_dump utility can be reloaded into later versions of PostgreSQL, which is not possible for file system level backups or continuous archiving.
  • An SQL dump is the only method that works when transferring a database to a different machine architecture, such as going from a 32-bit to a 64-bit server.
  • An SQL dump provides internally consistent dumps. A dump represents a snapshot of the database at the time pg_dump began running.
  • The pg_dump utility does not block other operations on the database when it is running.

A disadvantage of an SQL dump is that it takes more time compared to file system level backup.

9.3.5.1.2. Performing an SQL dump using pg_dump

To dump a single database without cluster-wide information, use the pg_dump utility.

Prerequisites

  • You must have read access to all tables that you want to dump. To dump the entire database, you must run the commands as the postgres superuser or a user with database administrator privileges.

Procedure

  • Dump a database without cluster-wide information: 

    $ pg_dump dbname > dumpfile

To specify which database server pg_dump will contact, use the following command-line options:

  • The -h option to define the host.

    The default host is either the local host or what is specified by the PGHOST environment variable.

  • The -p option to define the port.

    The default port is indicated by the PGPORT environment variable or the compiled-in default.

9.3.5.1.3. Performing an SQL dump using pg_dumpall

To dump each database in a given database cluster and to preserve cluster-wide data, use the pg_dumpall utility.

Prerequisites

  • You must run the commands as the postgres superuser or a user with database administrator privileges.

Procedure

  • Dump all databases in the database cluster and preserve cluster-wide data: 

    $ pg_dumpall > dumpfile

To specify which database server pg_dumpall will contact, use the following command-line options:

  • The -h option to define the host.

    The default host is either the local host or what is specified by the PGHOST environment variable.

  • The -p option to define the port.

    The default port is indicated by the PGPORT environment variable or the compiled-in default.

  • The -l option to define the default database.

    This option enables you to choose a default database different from the postgres database created automatically during initialization.

9.3.5.1.4. Restoring a database dumped using pg_dump

To restore a database from an SQL dump that you dumped using the pg_dump utility, follow the steps below.

Prerequisites

  • You must run the commands as the postgres superuser or a user with database administrator privileges.

Procedure

  1. Create a new database: 

    $ createdb dbname
  2. Make sure that all users who own objects or were granted permissions on objects in the dumped database already exist. If such users do not exist, the restore fails to recreate the objects with the original ownership and permissions.

  3. Run the psql utility to restore a text file dump created by the pg_dump utility: 

    $ psql dbname < dumpfile

    where dumpfile is the output of the pg_dump command. To restore a non-text file dump, use the pg_restore utility instead: 

    $ pg_restore non-plain-text-file
9.3.5.1.5. Restoring databases dumped using pg_dumpall

To restore data from a database cluster that you dumped using the pg_dumpall utility, follow the steps below.

Prerequisites

  • You must run the commands as the postgres superuser or a user with database administrator privileges.

Procedure

  1. Make sure that all users who own objects or were granted permissions on objects in the dumped databases already exist. If such users do not exist, the restore fails to recreate the objects with the original ownership and permissions.

  2. Run the psql utility to restore a text file dump created by the pg_dumpall utility: 

    $ psql < dumpfile

    where dumpfile is the output of the pg_dumpall command.

9.3.5.1.6. Performing an SQL dump of a database on another server

Dumping a database directly from one server to another is possible because pg_dump and psql can write to and read from pipes.

Procedure

  • To dump a database from one server to another, run: 

    $ pg_dump -h host1 dbname | psql -h host2 dbname
9.3.5.1.7. Handling SQL errors during restore

By default, psql continues to execute if an SQL error occurs, causing the database to restore only partially.

To change the default behavior, use one of the following approaches when restoring a dump.

Prerequisites

  • You must run the commands as the postgres superuser or a user with database administrator privileges.

Procedure

  • Make psql exit with an exit status of 3 if an SQL error occurs by setting the ON_ERROR_STOP variable: 

    $ psql --set ON_ERROR_STOP=on dbname < dumpfile

  • Specify that the whole dump is restored as a single transaction so that the restore is either fully completed or canceled.

    • When restoring a text file dump using the psql utility: 

      $ psql -1

    • When restoring a non-text file dump using the pg_restore utility: 

      $ pg_restore -e

      Note that when using this approach, even a minor error can cancel a restore operation that has already run for many hours.

9.3.5.1.8. Additional resources

9.3.5.2. Backing up PostgreSQL data with a file system level backup

To perform a file system level backup, copy PostgreSQL database files to another location. For example, you can use any of the following approaches:

  • Create an archive file using the tar utility.
  • Copy the files to a different location using the rsync utility.
  • Create a consistent snapshot of the data directory.
9.3.5.2.1. Advantages and disadvantages of a file system level backup

A file system level backup has the following advantage compared to other PostgreSQL backup methods:

  • File system level backup is usually faster than an SQL dump.

File system level backup has the following disadvantages compared to other PostgreSQL backup methods:

  • This backup method is not suitable when you want to upgrade from RHEL 7 to RHEL 8 and migrate your data to the upgraded system. File system level backup is architecture-specific and RHEL 7-specific. You can restore your data on your RHEL 7 system if the upgrade is not successful but you cannot restore the data on a RHEL 8 system.
  • The database server must be shut down before data backup and before data restore as well.
  • Backup and restore of certain individual files or tables is impossible. The file system backups only work for a complete backup and restoration of an entire database cluster.
9.3.5.2.2. Performing a file system level backup

To perform a file system level backup, use the following procedure.

Procedure

  1. Choose the location of a database cluster and initialize this cluster: 

    # postgresql-setup --initdb

  2. Stop the postgresql service: 

    # systemctl stop postgresql.service

  3. Use any method to make a file system backup, for example a tar archive: 

    $ tar -cf backup.tar /var/lib/pgsql/data

  4. Start the postgresql service: 

    # systemctl start postgresql.service
9.3.5.2.3. Additional resources

9.3.5.3. Backing up PostgreSQL data by continuous archiving

9.3.5.3.1. Introduction to continuous archiving

PostgreSQL records every change made to the database’s data files into a write ahead log (WAL) file that is available in the pg_wal/ subdirectory of the cluster’s data directory. This log is intended primarily for a crash recovery. After a crash, the log entries made since the last checkpoint can be used for restoring the database to a consistency.

The continuous archiving method, also known as an online backup, combines the WAL files with a copy of the database cluster in the form of a base backup performed on a running server or a file system level backup.

If a database recovery is needed, you can restore the database from the copy of the database cluster and then replay log from the backed up WAL files to bring the system to the current state.

With the continuous archiving method, you must keep a continuous sequence of all archived WAL files that extends at minimum back to the start time of your last base backup. Thus the ideal frequency of base backups depends on:

  • The storage volume available for archived WAL files.
  • The maximum possible duration of data recovery in situations when recovery is necessary. In cases with a long period since the last backup, the system replays more WAL segments, and the recovery thus takes more time.
Note

You cannot use pg_dump and pg_dumpall SQL dumps as a part of a continuous archiving backup solution. SQL dumps produce logical backups and do not contain enough information to be used by a WAL replay.

To perform a database backup and restore using the continuous archiving method, follow these instructions:

  1. Set up and test your procedure for archiving WAL files - see Section 9.3.5.3.3, “Setting up WAL archiving”.
  2. Perform a base backup - see Section 9.3.5.3.4, “Making a base backup”.

To restore your data, follow instructions in Section 9.3.5.3.5, “Restoring the database using a continuous archive backup”.

9.3.5.3.2. Advantages and disadvantages of continuous archiving

Continuous archiving has the following advantages compared to other PostgreSQL backup methods:

  • With the continuous backup method, it is possible to use a base backup that is not entirely consistent because any internal inconsistency in the backup is corrected by the log replay. Thus you can perform a base backup on a running PostgreSQL server.
  • A file system snapshot is not needed; tar or a similar archiving utility is sufficient.
  • Continuous backup can be achieved by continuing to archive the WAL files because the sequence of WAL files for the log replay can be indefinitely long. This is particularly valuable for large databases.
  • Continuous backup supports point-in-time recovery. It is not necessary to replay the WAL entries to the end. The replay can be stopped at any point and the database can be restored to its state at any time since the base backup was taken.
  • If the series of WAL files are continuously available to another machine that has been loaded with the same base backup file, it is possible to restore the other machine with a nearly-current copy of the database at any point.

Continuous archiving has the following disadvantages compared to other PostgreSQL backup methods:

  • Continuous backup method supports only restoration of an entire database cluster, not a subset.
  • Continuous backup requires extensive archival storage.
9.3.5.3.3. Setting up WAL archiving

A running PostgreSQL server produces a sequence of write ahead log (WAL) records. The server physically divides this sequence into WAL segment files, which are given numeric names that reflect their position in the WAL sequence. Without WAL archiving, the segment files are reused and renamed to higher segment numbers.

When archiving WAL data, the contents of each segment file are captured and saved at a new location before the segment file is reused. You have multiple options where to save the content, such as an NFS-mounted directory on another machine, a tape drive, or a CD.

Note that WAL records do not include changes to configuration files.

To enable WAL archiving, use the following procedure.

Procedure

  1. In the /var/lib/pgsql/data/postgresql.conf file:

    1. Set the wal_level configuration parameter to replica or higher.
    2. Set the archive_mode parameter to on.
    3. Specify the shell command in the archive_command configuration parameter. You can use the cp command, another command, or a shell script.

  2. Restart the postgresql service to enable the changes: 

    # systemctl restart postgresql.service
  3. Test your archive command and ensure it does not overwrite an existing file and that it returns a non-zero exit status if it fails.
  4. To protect your data, ensure that the segment files are archived into a directory that does not have group or world read access.
Note

The archive command is executed only on completed WAL segments. A server that generates little WAL traffic can have a substantial delay between the completion of a transaction and its safe recording in archive storage. To limit how old unarchived data can be, you can:

  • Set the archive_timeout parameter to force the server to switch to a new WAL segment file with a given frequency.
  • Use the pg_switch_wal parameter to force a segment switch to ensure that a transaction is archived immediately after it finishes.

Example 9.3. Shell command for archiving WAL segments

This example shows a simple shell command you can set in the archive_command configuration parameter.

The following command copies a completed segment file to the required location: 

archive_command = 'test ! -f /mnt/server/archivedir/%f && cp %p /mnt/server/archivedir/%f'

where the %p parameter is replaced by the relative path to the file to archive and the %f parameter is replaced by the file name.

This command copies archivable WAL segments to the /mnt/server/archivedir/ directory. After replacing the %p and %f parameters, the executed command looks as follows: 

test ! -f /mnt/server/archivedir/00000001000000A900000065 && cp pg_wal/00000001000000A900000065 /mnt/server/archivedir/00000001000000A900000065

A similar command is generated for each new file that is archived.

Additional resources

9.3.5.3.4. Making a base backup

You can create a base backup in several ways. This section describes the simplest way of performing a base backup using the pg_basebackup utility on a running PostgreSQL server.

The base backup process creates a backup history file that is stored into the WAL archive area and is named after the first WAL segment file that you need for the base backup.

The backup history file is a small text file containing the starting and ending times, and WAL segments of the backup. If you used the label string to identify the associated dump file, you can use the backup history file to determine which dump file to restore.

Note

Consider keeping several backup sets to be certain that you can recover your data.

To perform a base backup, use the following procedure.

Prerequisites

  • You must run the commands as the postgres superuser, a user with database administrator privileges, or another user with at least REPLICATION permissions.
  • You must keep all the WAL segment files generated during and after the base backup.

Procedure

  1. Use the pg_basebackup utility to perform the base backup.

    • To create a base backup as individual files (plain format): 

      $ pg_basebackup -D backup_directory -Fp

      Replace backup_directory with your desired backup location.

      If you use tablespaces and perform the base backup on the same host as the server, you must also use the --tablespace-mapping option, otherwise the backup will fail upon an attempt to write the backup to the same location.

    • To create a base backup as a tar archive (tar and compressed format): 

      $ pg_basebackup -D backup_directory -Ft -z

      Replace backup_directory with your desired backup location.

      To restore such data, you must manually extract the files in the correct locations.

  2. After the base backup process is complete, safely archive the copy of the database cluster and the WAL segment files used during the backup, which are specified in the backup history file.
  3. Delete WAL segments numerically lower than the WAL segment files used in the base backup because these are older than the base backup and no longer needed for a restore.

To specify which database server pg_basebackup will contact, use the following command-line options:

  • The -h option to define the host.

    The default host is either the local host or a host specified by the PGHOST environment variable.

  • The -p option to define the port.

    The default port is indicated by the PGPORT environment variable or the compiled-in default.

Additional resources

9.3.5.3.5. Restoring the database using a continuous archive backup

To restore a database using a continuous backup, use the following procedure.

Procedure

  1. Stop the server: 

    # systemctl stop postgresql.service

  2. Copy the necessary data to a temporary location.

    Preferably, copy the whole cluster data directory and any tablespaces. Note that this requires enough free space on your system to hold two copies of your existing database.

    If you do not have enough space, save the contents of the cluster’s pg_wal directory, which can contain logs that were not archived before the system went down.

  3. Remove all existing files and subdirectories under the cluster data directory and under the root directories of any tablespaces you are using.

  4. Restore the database files from your base backup.

    Make sure that:

    • The files are restored with the correct ownership (the database system user, not root).
    • The files are restored with the correct permissions.
    • The symbolic links in the pg_tblspc/ subdirectory are restored correctly.

  5. Remove any files present in the pg_wal/ subdirectory.

    These files resulted from the base backup and are therefore obsolete. If you did not archive pg_wal/, recreate it with proper permissions.

  6. Copy any unarchived WAL segment files that you saved in step 2 into pg_wal/.

  7. Create the recovery.conf recovery command file in the cluster data directory and specify the shell command in the restore_command configuration parameter. You can use the cp command, another command, or a shell script. For example: 

    restore_command = 'cp /mnt/server/archivedir/%f "%p"'

  8. Start the server: 

    # systemctl start postgresql.service

    The server will enter the recovery mode and proceed to read through the archived WAL files that it needs.

    If the recovery is terminated due to an external error, the server can be restarted and it will continue the recovery. When the recovery process is completed, the server renames recovery.conf to recovery.done. This prevents the server from accidental re-entering the recovery mode after it starts normal database operations.

  9. Check the contents of the database to make sure that the database has recovered into the required state.

    If the database has not recovered into the required state, return to step 1. If the database has recovered into the required state, allow the users to connect by restoring the client authentication configuration in the pg_hba.conf file.

For more information about restoring using the continuous backup, see PostgreSQL Documentation.

9.3.5.3.6. Additional resources

9.3.6. Migrating to a RHEL 8 version of PostgreSQL

Red Hat Enterprise Linux 7 contains PostgreSQL 9.2 as the default version of the PostgreSQL server. In addition, several versions of PostgreSQL are provided as Software Collections for RHEL 7.

Red Hat Enterprise Linux 8 provides PostgreSQL 10 (the default postgresql stream), PostgreSQL 9.6, PostgreSQL 12, and PostgreSQL 13.

Users of PostgreSQL on Red Hat Enterprise Linux can use two migration paths for the database files:

The fast upgrade method is quicker than the dump and restore process. However, in certain cases, the fast upgrade does not work, and you can only use the dump and restore process. Such cases include:

  • Cross-architecture upgrades
  • Systems using the plpython or plpython2 extensions. Note that RHEL 8 AppStream repository includes only the postgresql-plpython3 package, not the postgresql-plpython2 package.
  • Fast upgrade is not supported for migration from Red Hat Software Collections versions of PostgreSQL.

As a prerequisite for migration to a later version of PostgreSQL, back up all your PostgreSQL databases.

Dumping the databases and performing backup of the SQL files is required for the dump and restore process and recommended for the fast upgrade method.

Before migrating to a later version of PostgreSQL, see the upstream compatibility notes for the version of PostgreSQL to which you want to migrate, as well as for all skipped PostgreSQL versions between the one you are migrating from and the target version.

9.3.6.1. Fast upgrade using the pg_upgrade utility

During a fast upgrade, you must copy binary data files to the /var/lib/pgsql/data/ directory and use the pg_upgrade utility.

You can use this method for migrating data:

  • From the RHEL 7 system version of PostgreSQL 9.2 to the RHEL 8 version of PostgreSQL 10
  • From the RHEL 8 version of PostgreSQL 10 to the RHEL 8 version of PostgreSQL 12 or PostgreSQL 13

If you want to upgrade from an earlier postgresql stream within RHEL 8, follow the procedure described in Switching to a later stream and then migrate your PostgreSQL data.

For migrating between other combinations of PostgreSQL versions within RHEL, and for migration from the Red Hat Software Collections versions of PostgreSQL to RHEL, use Dump and restore upgrade.

The following procedure describes migration from the RHEL 7 system version of Postgreql 9.2 to a RHEL 8 version of PostgreSQL using the fast upgrade method.

Prerequisites

  • Before performing the upgrade, back up all your data stored in the PostgreSQL databases. By default, all data is stored in the /var/lib/pgsql/data/ directory on both the RHEL 7 and RHEL 8 systems.

Procedure

  1. On the RHEL 8 system, enable the stream (version) to which you wish to migrate: 

    # yum module enable postgresql:stream

    Replace stream with the selected version of the PostgreSQL server.

    You can omit this step if you want to use the default stream, which provides PostgreSQL 10.

  2. On the RHEL 8 system, install the postgresql-server and postgresql-upgrade packages: 

    # yum install postgresql-server postgresql-upgrade

    Optionally, if you used any PostgreSQL server modules on RHEL 7, install them also on the RHEL 8 system in two versions, compiled both against PostgreSQL 9.2 (installed as the postgresql-upgrade package) and the target version of PostgreSQL (installed as the postgresql-server package). If you need to compile a third-party PostgreSQL server module, build it both against the postgresql-devel and postgresql-upgrade-devel packages.

  3. Check the following items:

    • Basic configuration: On the RHEL 8 system, check whether your server uses the default /var/lib/pgsql/data directory and the database is correctly initialized and enabled. In addition, the data files must be stored in the same path as mentioned in the /usr/lib/systemd/system/postgresql.service file.
    • PostgreSQL servers: Your system can run multiple PostgreSQL servers. Make sure that the data directories for all these servers are handled independently.
    • PostgreSQL server modules: Ensure that the PostgreSQL server modules that you used on RHEL 7 are installed on your RHEL 8 system as well. Note that plug-ins are installed in the /usr/lib64/pgsql/ directory (or in the /usr/lib/pgsql/ directory on 32-bit systems).

  4. Ensure that the postgresql service is not running on either of the source and target systems at the time of copying data. 

    # systemctl stop postgresql.service
  5. Copy the database files from the source location to the /var/lib/pgsql/data/ directory on the RHEL 8 system.

  6. Perform the upgrade process by running the following command as the PostgreSQL user: 

    # postgresql-setup --upgrade

    This launches the pg_upgrade process in the background.

    In case of failure, postgresql-setup provides an informative error message.

  7. Copy the prior configuration from /var/lib/pgsql/data-old to the new cluster.

    Note that the fast upgrade does not reuse the prior configuration in the newer data stack and the configuration is generated from scratch. If you want to combine the old and new configurations manually, use the *.conf files in the data directories.

  8. Start the new PostgreSQL server: 

    # systemctl start postgresql.service

  9. Run the analyze_new_cluster.sh script located in the PostgreSQL home directory: 

    su postgres -c '~/analyze_new_cluster.sh'

  10. If you want the new PostgreSQL server to be automatically started on boot, run: 

    # systemctl enable postgresql.service

9.3.6.2. Dump and restore upgrade

When using the dump and restore upgrade, you must dump all databases contents into an SQL file dump file.

Note that the dump and restore upgrade is slower than the fast upgrade method and it may require some manual fixing in the generated SQL file.

You can use this method for migrating data from:

  • The Red Hat Enterprise Linux 7 system version of PostgreSQL 9.2
  • Any earlier Red Hat Enterprise Linux 8 version of PostgreSQL

  • An earlier or equal version of PostgreSQL from Red Hat Software Collections:

    • PostgreSQL 9.2 (no longer supported)
    • PostgreSQL 9.4 (no longer supported)
    • PostgreSQL 9.6 (no longer supported)
    • PostgreSQL 10
    • PostgreSQL 12

On RHEL 7 and RHEL 8 systems, PostgreSQL data is stored in the /var/lib/pgsql/data/ directory by default. In case of Red Hat Software Collections versions of PostgreSQL, the default data directory is /var/opt/rh/collection_name/lib/pgsql/data/ (with the exception of postgresql92, which uses the /opt/rh/postgresql92/root/var/lib/pgsql/data/ directory).

If you want to upgrade from an earlier postgresql stream within RHEL 8, follow the procedure described in Switching to a later stream and then migrate your PostgreSQL data.

To perform the dump and restore upgrade, change the user to root.

The following procedure describes migration from the RHEL 7 system version of Postgreql 9.2 to a RHEL 8 version of PostgreSQL.

Procedure

  1. On your RHEL 7 system, start the PostgreSQL 9.2 server: 

    # systemctl start postgresql.service

  2. On the RHEL 7 system, dump all databases contents into the pgdump_file.sql file: 

    su - postgres -c "pg_dumpall > ~/pgdump_file.sql"

  3. Make sure that the databases were dumped correctly: 

    su - postgres -c 'less "$HOME/pgdump_file.sql"'

    As a result, the path to the dumped sql file is displayed: /var/lib/pgsql/pgdump_file.sql.

  4. On the RHEL 8 system, enable the stream (version) to which you wish to migrate: 

    # yum module enable postgresql:stream

    Replace stream with the selected version of the PostgreSQL server.

    You can omit this step if you want to use the default stream, which provides PostgreSQL 10.

  5. On the RHEL 8 system, install the postgresql-server package: 

    # yum install postgresql-server

    Optionally, if you used any PostgreSQL server modules on RHEL 7, install them also on the RHEL 8 system. If you need to compile a third-party PostgreSQL server module, build it against the postgresql-devel package.

  6. On the RHEL 8 system, initialize the data directory for the new PostgreSQL server: 

    # postgresql-setup --initdb

  7. On the RHEL 8 system, copy the pgdump_file.sql into the PostgreSQL home directory, and check that the file was copied correctly: 

    su - postgres -c 'test -e "$HOME/pgdump_file.sql" && echo exists'

  8. Copy the configuration files from the RHEL 7 system: 

    su - postgres -c 'ls -1 $PGDATA/*.conf'

    The configuration files to be copied are:

    • /var/lib/pgsql/data/pg_hba.conf
    • /var/lib/pgsql/data/pg_ident.conf
    • /var/lib/pgsql/data/postgresql.conf

  9. On the RHEL 8 system, start the new PostgreSQL server: 

    # systemctl start postgresql.service

  10. On the RHEL 8 system, import data from the dumped sql file: 

    su - postgres -c 'psql -f ~/pgdump_file.sql postgres'
Note

When upgrading from a Red Hat Software Collections version of PostgreSQL, adjust the commands to include scl enable collection_name. For example, to dump data from the rh-postgresql96 Software Collection, use the following command: 

su - postgres -c 'scl enable rh-postgresql96 "pg_dumpall > ~/pgdump_file.sql"'