pg_upgrade (formerly called pg_migrator) allows data stored in PostgreSQL data files to be upgraded to a later PostgreSQL major version without the data dump/reload typically required for major version upgrades, e.g. from 8.4.7 to the current major release of PostgreSQL. It is not required for minor version upgrades, e.g. from 9.0.1 to 9.0.4.
Major PostgreSQL releases regularly add new features that often change the layout of the system tables, but the internal data storage format rarely changes. pg_upgrade uses this fact to perform rapid upgrades by creating new system tables and simply reusing the old user data files. If a future major release ever changes the data storage format in a way that makes the old data format unreadable, pg_upgrade will not be usable for such upgrades. (The community will attempt to avoid such situations.)
pg_upgrade does its best to make sure the old and new clusters are binary-compatible, e.g. by checking for compatible compile-time settings, including 32/64-bit binaries. It is important that any external modules are also binary compatible, though this cannot be checked by pg_upgrade.
pg_upgrade supports upgrades from 8.4.X and later to the current major release of PostgreSQL, including snapshot and alpha releases.
pg_upgrade accepts the following command-line arguments:
the old PostgreSQL executable directory; environment variable PGBINOLD
the new PostgreSQL executable directory; environment variable PGBINNEW
check clusters only, don't change any data
the old cluster data directory; environment variable PGDATAOLD
the new cluster data directory; environment variable PGDATANEW
number of simultaneous processes or threads to use
use hard links instead of copying files to the new cluster
options to be passed directly to the old postgres command; multiple option invocations are appended
options to be passed directly to the new postgres command; multiple option invocations are appended
the old cluster port number; environment variable PGPORTOLD
the new cluster port number; environment variable PGPORTNEW
retain SQL and log files even after successful completion
cluster's install user name; environment variable PGUSER
enable verbose internal logging
display version information, then exit
show help, then exit
These are the steps to perform an upgrade with pg_upgrade:
Optionally move the old cluster
If you are using a version-specific installation directory, e.g. /opt/PostgreSQL/9.1, you do not need to move the old cluster. The graphical installers all use version-specific installation directories.
If your installation directory is not version-specific, e.g. /usr/local/pgsql, it is necessary to move the current PostgreSQL install directory so it does not interfere with the new PostgreSQL installation. Once the current PostgreSQL server is shut down, it is safe to rename the PostgreSQL installation directory; assuming the old directory is /usr/local/pgsql, you can do:
mv /usr/local/pgsql /usr/local/pgsql.old
to rename the directory.
For source installs, build the new version
Build the new PostgreSQL source with configure flags that are compatible with the old cluster. pg_upgrade will check pg_controldata to make sure all settings are compatible before starting the upgrade.
Install the new PostgreSQL binaries
Install the new server's binaries and support files. pg_upgrade is included in a default installation.
For source installs, if you wish to install the new server in a custom location, use the prefix variable:
make prefix=/usr/local/pgsql.new install
Initialize the new PostgreSQL cluster
Initialize the new cluster using initdb. Again, use compatible initdb flags that match the old cluster. Many prebuilt installers do this step automatically. There is no need to start the new cluster.
Install custom shared object files
Install any custom shared object files (or DLLs) used by the old cluster into the new cluster, e.g. pgcrypto.so, whether they are from contrib or some other source. Do not install the schema definitions, e.g. CREATE EXTENSION pgcrypto, because these will be upgraded from the old cluster. Also, any custom full text search files (dictionary, synonym, thesaurus, stop words) must also be copied to the new cluster.
pg_upgrade will connect to the old and new servers several times, so you might want to set authentication to peer in pg_hba.conf or use a ~/.pgpass file (see Section 31.15).
Stop both servers
Make sure both database servers are stopped using, on Unix, e.g.:
pg_ctl -D /opt/PostgreSQL/8.4 stop pg_ctl -D /opt/PostgreSQL/9.0 stop
or on Windows, using the proper service names:
NET STOP postgresql-8.4 NET STOP postgresql-9.0
Streaming replication and log-shipping standby servers can remain running until a later step.
Prepare for standby server upgrades
If you are upgrading standby servers using methods outlined in section step 10, verify that the old standby servers are caught up by running pg_controldata against the old primary and standby clusters. Verify that the "Latest checkpoint location" values match in all clusters. (There will be a mismatch if old standby servers were shut down before the old primary or if the old standby servers are still running.) Also, change wal_level to hot_standby in the postgresql.conf file on the new primary cluster.
Always run the pg_upgrade binary of the new server, not the old one. pg_upgrade requires the specification of the old and new cluster's data and executable (bin) directories. You can also specify user and port values, and whether you want the data linked instead of copied (the default).
If you use link mode, the upgrade will be much faster (no file copying) and use less disk space, but you will not be able to access your old cluster once you start the new cluster after the upgrade. Link mode also requires that the old and new cluster data directories be in the same file system. (Tablespaces and pg_xlog can be on different file systems.) See pg_upgrade --help for a full list of options.
The --jobs option allows multiple CPU cores to be used for copying/linking of files and to dump and reload database schemas in parallel; a good place to start is the maximum of the number of CPU cores and tablespaces. This option can dramatically reduce the time to upgrade a multi-database server running on a multiprocessor machine.
For Windows users, you must be logged into an administrative account, and then start a shell as the postgres user and set the proper path:
RUNAS /USER:postgres "CMD.EXE" SET PATH=%PATH%;C:\Program Files\PostgreSQL\9.0\bin;
and then run pg_upgrade with quoted directories, e.g.:
pg_upgrade.exe --old-datadir "C:/Program Files/PostgreSQL/8.4/data" --new-datadir "C:/Program Files/PostgreSQL/9.0/data" --old-bindir "C:/Program Files/PostgreSQL/8.4/bin" --new-bindir "C:/Program Files/PostgreSQL/9.0/bin"
Once started, pg_upgrade will verify the two clusters are compatible and then do the upgrade. You can use pg_upgrade --check to perform only the checks, even if the old server is still running. pg_upgrade --check will also outline any manual adjustments you will need to make after the upgrade. If you are going to be using link mode, you should use the --link option with --check to enable link-mode-specific checks. pg_upgrade requires write permission in the current directory.
Obviously, no one should be accessing the clusters during the upgrade. pg_upgrade defaults to running servers on port 50432 to avoid unintended client connections. You can use the same port number for both clusters when doing an upgrade because the old and new clusters will not be running at the same time. However, when checking an old running server, the old and new port numbers must be different.
If an error occurs while restoring the database schema, pg_upgrade will exit and you will have to revert to the old cluster as outlined in step 16 below. To try pg_upgrade again, you will need to modify the old cluster so the pg_upgrade schema restore succeeds. If the problem is a contrib module, you might need to uninstall the contrib module from the old cluster and install it in the new cluster after the upgrade, assuming the module is not being used to store user data.
Upgrade Streaming Replication and Log-Shipping standby servers
If you used link mode and have Streaming Replication (see Section 25.2.5) or Log-Shipping (see Section 25.2) standby servers, you can follow these steps to quickly upgrade them. You will not be running pg_upgrade on the standby servers, but rather rsync on the primary. Do not start any servers yet.
If you did not use link mode, do not have or do not want to use rsync, or want an easier solution, skip the instructions in this section and simply recreate the standby servers once pg_upgrade completes and the new primary is running.
Install the new PostgreSQL binaries on standby servers
Make sure the new binaries and support files are installed on all standby servers.
Make sure the new standby data directories do not exist
Make sure the new standby data directories do not exist or are empty. If initdb was run, delete the standby servers' new data directories.
Install custom shared object files
Install the same custom shared object files on the new standbys that you installed in the new primary cluster.
Stop standby servers
If the standby servers are still running, stop them now using the above instructions.
Save configuration files
Save any configuration files from the old standbys' data directories you need to keep, e.g. postgresql.conf, recovery.conf, because these will be overwritten or removed in the next step.
When using link mode, standby servers can be quickly upgraded using rsync. To accomplish this, from a directory on the primary server that is above the old and new database cluster directories, run this on the primary for each standby server:
rsync --archive --delete --hard-links --size-only --no-inc-recursive old_cluster new_cluster remote_dir
where old_cluster and new_cluster are relative to the current directory on the primary, and remote_dir is above the old and new cluster directories on the standby. The directory structure under the specified directories on the primary and standbys must match. Consult the rsync manual page for details on specifying the remote directory, e.g.
rsync --archive --delete --hard-links --size-only --no-inc-recursive /opt/PostgreSQL/9.5 \ /opt/PostgreSQL/9.6 standby.example.com:/opt/PostgreSQL
You can verify what the command will do using rsync's --dry-run option. While rsync must be run on the primary for at least one standby, it is possible to run rsync on an upgraded standby to upgrade other standbys, as long as the upgraded standby has not been started.
What this does is to record the links created by pg_upgrade's link mode that connect files in the old and new clusters on the primary server. It then finds matching files in the standby's old cluster and creates links for them in the standby's new cluster. Files that were not linked on the primary are copied from the primary to the standby. (They are usually small.) This provides rapid standby upgrades. Unfortunately, rsync needlessly copies files associated with temporary and unlogged tables because these files don't normally exist on standby servers.
If you have tablespaces, you will need to run a similar rsync command for each tablespace directory, e.g.:
rsync --archive --delete --hard-links --size-only --no-inc-recursive /vol1/pg_tblsp/PG_9.5_201510051 \ /vol1/pg_tblsp/PG_9.6_201608131 standby.example.com:/vol1/pg_tblsp
If you have relocated pg_xlog outside the data directories, rsync must be run on those directories too.
Configure streaming replication and log-shipping standby servers
Configure the servers for log shipping. (You do not need to run
pg_stop_backup() or take a file system backup as the standbys are still synchronized with the primary.)
If you modified pg_hba.conf, restore its original settings. It might also be necessary to adjust other configuration files in the new cluster to match the old cluster, e.g. postgresql.conf.
Start the new server
The new server can now be safely started, and then any rsync'ed standby servers.
If any post-upgrade processing is required, pg_upgrade will issue warnings as it completes. It will also generate script files that must be run by the administrator. The script files will connect to each database that needs post-upgrade processing. Each script should be run using:
psql --username postgres --file script.sql postgres
The scripts can be run in any order and can be deleted once they have been run.
In general it is unsafe to access tables referenced in rebuild scripts until the rebuild scripts have run to completion; doing so could yield incorrect results or poor performance. Tables not referenced in rebuild scripts can be accessed immediately.
Because optimizer statistics are not transferred by pg_upgrade, you will be instructed to run a command to regenerate that information at the end of the upgrade. You might need to set connection parameters to match your new cluster.
Delete old cluster
Once you are satisfied with the upgrade, you can delete the old cluster's data directories by running the script mentioned when pg_upgrade completes. (Automatic deletion is not possible if you have user-defined tablespaces inside the old data directory.) You can also delete the old installation directories (e.g. bin, share).
Reverting to old cluster
If, after running pg_upgrade, you wish to revert to the old cluster, there are several options:
If the --check option was used, the old cluster was unmodified; it can be restarted.
If the --link option was not used, the old cluster was unmodified; it can be restarted.
If the --link option was used, the data files might be shared between the old and new cluster:
If pg_upgrade aborted before linking started, the old cluster was unmodified; it can be restarted.
If you did not start the new cluster, the old cluster was unmodified except that, when linking started, a .old suffix was appended to $PGDATA/global/pg_control. To reuse the old cluster, remove the .old suffix from $PGDATA/global/pg_control; you can then restart the old cluster.
If you did start the new cluster, it has written to shared files and it is unsafe to use the old cluster. The old cluster will need to be restored from backup in this case.
pg_upgrade does not support upgrading of databases containing these reg* OID-referencing system data types: regproc, regprocedure, regoper, regoperator, regconfig, and regdictionary. (regtype can be upgraded.)
All failure, rebuild, and reindex cases will be reported by pg_upgrade if they affect your installation; post-upgrade scripts to rebuild tables and indexes will be generated automatically. If you are trying to automate the upgrade of many clusters, you should find that clusters with identical database schemas require the same post-upgrade steps for all cluster upgrades; this is because the post-upgrade steps are based on the database schemas, and not user data.
For deployment testing, create a schema-only copy of the old cluster, insert dummy data, and upgrade that.
If you are upgrading a pre-PostgreSQL 9.2 cluster that uses a configuration-file-only directory, you must pass the real data directory location to pg_upgrade, and pass the configuration directory location to the server, e.g. -d /real-data-directory -o '-D /configuration-directory'.
If using a pre-9.1 old server that is using a non-default Unix-domain socket directory or a default that differs from the default of the new cluster, set PGHOST to point to the old server's socket location. (This is not relevant on Windows.)
If you want to use link mode and you do not want your old cluster to be modified when the new cluster is started, make a copy of the old cluster and upgrade that in link mode. To make a valid copy of the old cluster, use rsync to create a dirty copy of the old cluster while the server is running, then shut down the old server and run rsync --checksum again to update the copy with any changes to make it consistent. (--checksum is necessary because rsync only has file modification-time granularity of one second.) You might want to exclude some files, e.g. postmaster.pid, as documented in Section 24.3.3. If your file system supports file system snapshots or copy-on-write file copies, you can use that to make a backup of the old cluster and tablespaces, though the snapshot and copies must be created simultaneously or while the database server is down.
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